Adaptation of transmit power based on channel quality

ABSTRACT

Transmit power (e.g., maximum transmit power) may be defined based on the maximum received signal strength allowed by a receiver and a minimum coupling loss from a transmitting node to a receiver. Transmit power may be defined for an access node (e.g., a femto node) such that a corresponding outage created in a cell (e.g., a macro cell) is limited while still providing an acceptable level of coverage for access terminals associated with the access node. An access node may autonomously adjust its transmit power based on channel measurement and a defined coverage hole to mitigate interference. Transmit power may be defined based on channel quality. Transmit power may be defined based on a signal-to-noise ratio at an access terminal. The transmit power of neighboring access nodes also may be controlled by inter-access node signaling.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims the benefit of and priority to commonly ownedU.S. Provisional Patent Application No. 60/955,301, filed Aug. 10, 2007,and U.S. Provisional Patent Application No. 60/957,967, filed Aug. 24,2007, the disclosure of each of which is hereby incorporated byreference herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to concurrently filed and commonly ownedU.S. patent application Ser. No. 12/187,307, entitled “ADAPTATION OFTRANSMIT POWER BASED ON MAXIMUM RECEIVED SIGNAL STRENGTH”; U.S. patentapplication Ser. No. 12/187,310, entitled “AUTONOMOUS ADAPTATION OFTRANSMIT POWER”; and U.S. patent application Ser. No. 12/187,304,entitled “ADAPTATION OF TRANSMIT POWER FOR NEIGHBORING NODES”; thedisclosure of which is hereby incorporated by reference herein.

BACKGROUND

1. Field

This application relates generally to wireless communication and morespecifically, but not exclusively, to improving communicationperformance.

2. Introduction

Wireless communication systems are widely deployed to provide varioustypes of communication (e.g., voice, data, multimedia services, etc.) tomultiple users. As the demand for high-rate and multimedia data servicesrapidly grows, there lies a challenge to implement efficient and robustcommunication systems with enhanced performance.

To supplement the base stations of a conventional mobile phone network(e.g., a macro cellular network), small-coverage base stations may bedeployed, for example, in a user's home. Such small-coverage basestations are generally known as access point base stations, home NodeBs,or femto cells and may be used to provide more robust indoor wirelesscoverage to mobile units. Typically, such small-coverage base stationsare connected to the Internet and the mobile operator's network via aDSL router or a cable modem.

In a typical macro cellular deployment the RF coverage is planned andmanaged by cellular network operators to optimize coverage. Femto basestations, on the other hand, may be installed by the subscriberpersonally and deployed in an ad-hoc manner. Consequently, femto cellsmay cause interference both on the uplink (“UL”) and downlink (“DL”) ofthe macro cells. For example, a femto base station installed near awindow of a residence may cause significant downlink interference to anyaccess terminals outside the house that are not served by the femtocell. Also, on the uplink, home access terminals that are served by afemto cell may cause interference at a macro cell base station (e.g.,macro NodeB).

Interference between the macro and femto deployments may be mitigated byoperating the femto network on a separate RF carrier frequency than themacro cellular network.

Femto cells also may interfere with one another as a result of unplanneddeployment. For example, in a multi-resident apartment, a femto basestation installed near a wall separating two residences may causesignificant interference to a neighboring residence. Here, the strongestfemto base station seen by a home access terminal (e.g., strongest interms of RF signal strength received at the access terminal) may notnecessarily be the serving base station for the access terminal due to arestricted association policy enforced by that femto base station.

RF interference issues may thus arise in a communication system whereradio frequency (“RF”) coverage of femto base stations is not optimizedby the mobile operator and where deployment of such base stations isad-hoc. Thus, there is a need for improved interference management forwireless networks.

SUMMARY

A summary of sample aspects of the disclosure follows. It should beunderstood that any reference to the term aspects herein may refer toone or more aspects of the disclosure.

The disclosure relates in some aspect to determining transmit power(e.g., maximum power) based on the maximum received signal strengthallowed by a receiver and based on a minimum coupling loss from atransmitting node to a receiver. In this way, desensitization of thereceiver may be avoided in a system where there is a relatively smallpath loss between these components (e.g., where the receiver may bearbitrarily close to the transmitter).

The disclosure relates in some aspects to defining transmit power for anaccess node (e.g., a femto node) such that a corresponding outage (e.g.,a coverage hole) created in a cell (e.g., a macro cell) is limited whilestill providing an acceptable level of coverage for access terminalsassociated with the access node. In some aspects, these techniques maybe employed for coverage holes in adjacent channels (e.g., implementedon adjacent RF carriers) and in co-located channels (e.g., implementedon the same RF carrier).

The disclosure relates in some aspects to autonomously adjustingdownlink transmit power at an access node (e.g., a femto node) tomitigate interference. In some aspects, the transmit power is adjustedbased on channel measurement and a defined coverage hole. Here, a mobileoperator may specify coverage hole and/or channel characteristics usedto adjust the transmit power.

In some implementations an access node measures (or receives anindication of) the received signal strength of signals from a macroaccess node and predicts a path loss relating to the coverage hole inthe macro cell (e.g., corrected for penetration loss, etc.). Based on acoverage target (path loss), the access node may select a particulartransmit power value. For example, transmit power at the access node maybe adjusted based on measured macro signal strength (e.g., RSCP) andtotal signal strength (e.g., RSSI) measured at a macro node level.

The disclosure relates in some aspects to defining transmit power basedon channel quality. For example, an access node may commence operationwith a default transmit power (e.g., pilot fraction value) when it isinstalled and later dynamically adjust the transmit power based onDRC/CQI feedback from an access terminal. In some aspects, if requestedDRC over a long time period is always very high, this is an indicationthat the PF value may be too high and the access node may elect tooperate at lower value.

The disclosure relates in some aspects to defining transmit power basedon signal-to-noise ratio at an access terminal. For example, a maximumtransmit power may be defined for an access node to ensure that thesignal-to-noise ratio at an associated access terminal does not exceed adefined maximum value when the access terminal is at or near an edge ofa coverage area for the access node.

The disclosure relates in some aspects to adaptively adjusting thedownlink transmit power of neighboring access nodes. In some aspects,sharing of information between access nodes may be utilized to enhancenetwork performance. For example, if an access terminal is experiencinghigh interference levels from a neighboring access node, informationrelating to this interference may be relayed to the neighbor access nodevia the home access node of the access terminal. As a specific example,the access terminal may send a neighbor report to its home access node,whereby the report indicates the received signal strength the accessterminal sees from neighboring access nodes. The access node may thendetermine whether the home access terminal is being unduly interferedwith by one of the access nodes in the neighbor report. If so, theaccess node may send a message to the interfering access node requestingthat the access node reduce its transmit power. Similar functionalitymay be achieved through the use of a centralized power controller.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other sample aspects of the disclosure will be described inthe detailed description and the appended claims that follow, and in theaccompanying drawings, wherein:

FIG. 1 is a simplified diagram of several sample aspects of acommunication system including macro coverage and smaller scalecoverage;

FIG. 2 is a simplified block diagram of several sample aspects of anaccess node;

FIG. 3 is a flowchart of several sample aspects of operations that maybe performed to determine transmit power based on maximum receivedsignal strength of a receiver and minimum coupling loss;

FIG. 4 is a flowchart of several sample aspects of operations that maybe performed to determine transmit power based on one or more channelconditions;

FIG. 5 is a flowchart of several sample aspects of operations that maybe performed to determine transmit power based on total received signalstrength;

FIG. 6 is a flowchart of several sample aspects of operations that maybe performed to determine transmit power based on signal-to-noise ratio;

FIG. 7 is a simplified diagram illustrating coverage areas for wirelesscommunication;

FIG. 8 is a simplified diagram of several sample aspects of acommunication system including neighboring femto cells;

FIG. 9 is a flowchart of several sample aspects of operations that maybe performed to control transmit power of a neighboring access node;

FIG. 10 is a flowchart of several sample aspects of operations that maybe performed to adjust transmit power in response to a request fromanother node;

FIG. 11 is a simplified diagram of several sample aspects of acommunication system including centralized power control;

FIG. 12 is a flowchart of several sample aspects of operations that maybe performed to control transmit power of an access node usingcentralized power control;

FIGS. 13A and 13B are a flowchart of several sample aspects ofoperations that may be performed to control transmit power of an accessnode using centralized power control;

FIG. 14 is a simplified diagram of a wireless communication systemincluding femto nodes;

FIG. 15 is a simplified block diagram of several sample aspects ofcommunication components; and

FIGS. 16-19 are simplified block diagrams of several sample aspects ofapparatuses configured to provide power control as taught herein.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may be simplified for clarity. Thus,the drawings may not depict all of the components of a given apparatus(e.g., device) or method. Finally, like reference numerals may be usedto denote like features throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein is merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. Furthermore,an aspect may comprise at least one element of a claim.

FIG. 1 illustrates sample aspects of a network system 100 that includesmacro scale coverage (e.g., a large area cellular network such as a 3Gnetwork, which may be commonly referred to as a macro cell network) andsmaller scale coverage (e.g., a residence-based or building-basednetwork environment). As a node such as access terminal 102A movesthrough the network, the access terminal 102A may be served in certainlocations by access nodes (e.g., access node 104) that provide macrocoverage as represented by the area 106 while the access terminal 102Amay be served at other locations by access nodes (e.g., access node 108)that provide smaller scale coverage as represented by the area 110. Insome aspects, the smaller coverage nodes may be used to provideincremental capacity growth, in-building coverage, and differentservices (e.g., for a more robust user experience).

As will be discussed in more detail below, the access node 108 may berestricted in that it may not provide certain services to certain nodes(e.g., a visitor access terminal 102B). As a result, a coverage hole(e.g., corresponding to the coverage area 110) may be created in themacro coverage area 104.

The size of the coverage hole may depend on whether the access node 104and the access node 108 are operating on the same frequency carrier. Forexample, when the nodes 104 and 108 are on a co-channel (e.g., using thesame frequency carrier), the coverage hole may correspond to thecoverage area 110. Thus, in this case the access terminal 102A may losemacro coverage when it is within the coverage area 110 (e.g., asindicated by the phantom view of the access terminal 102B).

When the nodes 104 and 108 are on adjacent channels (e.g., usingdifferent frequency carriers), a smaller coverage hole 112 may becreated in the macro coverage area 104 as a result of adjacent channelinterference from the access node 108. Thus, when the access terminal102A is operating on an adjacent channel, the access terminal 102A mayreceive macro coverage at a location that is closer to the access node108 (e.g., just outside the coverage area 112).

Depending on system design parameters, the co-channel coverage hole maybe relatively large. For example, if the interference of the access node108 is at least as low as the thermal noise floor, the coverage hole mayhave a radius on the order of 40 meters for a CDMA system where thetransmit power of the access node 108 is 0 dBm, assuming free spacepropagation loss and a worst case where there is no wall separationbetween the nodes 108 and 102B.

A tradeoff thus exists between minimizing the outage in the macrocoverage while maintaining adequate coverage within a designated smallerscale environment (e.g., femto node coverage inside a home). Forexample, when a restricted femto node is at the edge of the macrocoverage, as a visiting access terminal approaches the femto node, thevisiting access terminal is likely to lose macro coverage and drop thecall. In such a case, one solution for the macro cellular network wouldbe to move the visitor access terminal to another carrier (e.g., wherethe adjacent channel interference from the femto node is small). Due tolimited spectrum available to each operator, however, the use ofseparate carrier frequencies may not always be practical. In any event,another operator may be using the carrier used by the femto node.Consequently, a visitor access terminal associated with that otheroperator may suffer from the coverage hole created by the restrictedfemto node on that carrier.

As will be described in detail in conjunction with FIGS. 2-13B, atransmit power value for a node may be defined to manage suchinterference and/or address other similar issues. In someimplementations, the defined transmit power may relate to at least oneof: a maximum transmit power, transmit power for a femto node, ortransmit power for transmitting a pilot signal (e.g., as indicated by apilot fraction value).

For convenience, the following describes various scenarios wheretransmit power is defined for a femto node deployed within a macronetwork environment. Here, the term macro node refers in some aspects toa node that provides coverage over a relatively large area. The termfemto node refers in some aspects to a node that provides coverage overa relatively small area (e.g., a residence). A node that providescoverage over an area that is smaller than a macro area and larger thana femto area may be referred to as a pico node (e.g., providing coveragewithin a commercial building). It should be appreciated that theteachings herein may be implemented with various types of nodes andsystems. For example, a pico node or some other type of nod may providethe same or similar functionality as a femto node for a different (e.g.,larger) coverage area. Thus, a pico node may be restricted, a pico nodemay be associated with one or more home access terminals, and so on.

In various applications, other terminology may be used to reference amacro node, a femto node, or a pico node. For example, a macro node maybe configured or referred to as an access node, base station, accesspoint, eNodeB, macro cell, macro NodeB (“MNB”), and so on. Also, a femtonode may be configured or referred to as a home NodeB (“HNB”), homeeNodeB, access point base station, femto cell, and so on. Also, a cellassociated with a macro node, a femto node, or a pico node may bereferred to as a macro cell, a femto cell, or a pico cell, respectively.In some implementations, each cell may be further associated with (e.g.,divided into) one or more sectors.

As mentioned above, a femto node may be restricted in some aspects. Forexample, a given femto node may only provide service to a limited set ofaccess terminals. Thus, in deployments with so-called restricted (orclosed) association, a given access terminal may be served by the macrocell mobile network and a limited set of femto nodes (e.g., femto nodesthat reside within a corresponding user residence).

The restricted provisioned set of access terminals associated arestricted femto node (which may also be referred to as a ClosedSubscriber Group Home NodeB) may be temporarily or permanently extendedas necessary. In some aspects, a Closed Subscriber Group (“CSG”) may bedefined as the set of access nodes (e.g., femto nodes) that share acommon access control list of access terminals. In some implementations,all femto nodes (or all restricted femto nodes) in a region may operateon a designated channel, which may be referred to as the femto channel.

Various relationships may be defined between a restricted femto node anda given access terminal. For example, from the perspective of an accessterminal, an open femto node may refer to a femto node with norestricted association. A restricted femto node may refer to a femtonode that is restricted in some manner (e.g., restricted for associationand/or registration). A home femto node may refer to a femto node onwhich the access terminal is authorized to access and operate. A guestfemto node may refer to a femto node on which an access terminal istemporarily authorized to access or operate. An alien femto node mayrefer to a femto node on which the access terminal is not authorized toaccess or operate, except for perhaps emergency situations (e.g., 911calls).

From the perspective of a restricted femto node, a home access terminal(or home user equipment, “HUE”) may refer to an access terminal that isauthorized to access the restricted femto node. A guest access terminalmay refer to an access terminal with temporary access to the restrictedfemto node. An alien access terminal may refer to an access terminalthat does not have permission to access the restricted femto node,except for perhaps emergency situations such as 911 calls. Thus, in someaspects an alien access terminal may be defined as one that does nothave the credentials or permission to register with the restricted femtonode. An access terminal that is currently restricted (e.g., deniedaccess) by a restricted femto cell may be referred to herein as avisitor access terminal. A visitor access terminal may thus correspondto an alien access terminal and, when service is not allowed, a guestaccess terminal.

FIG. 2 illustrates various components of an access node 200 (hereafterreferred to as femto node 200) that may be used in one or moreimplementations as taught herein. For example, different configurationsof the components depicted in FIG. 2 may be employed for the differentexamples of FIGS. 3-13B. It should thus be appreciated that in someimplementations a node may not incorporate all of the componentsdepicted in FIG. 2 while in other implementations (e.g., where a nodeuses multiple algorithms to determine a maximum transmit power) a nodemay employ most or all of the components depicted in FIG. 2.

Briefly, the femto node 200 includes a transceiver 202 for communicatingwith other nodes (e.g., access terminals). The transceiver 202 includesa transmitter 204 for sending signals and a receiver 206 for receivingsignals. The femto node 200 also includes a transmit power controller208 for determining transmit power (e.g., maximum transmit power) forthe transmitter 204. The femto node 200 includes a communicationcontroller 210 for managing communications with other nodes and forproviding other related functionality as taught herein. The femto node200 includes one or more data memories 212 for storing variousinformation. The femto node 200 also may include an authorizationcontroller 210 for managing access to other nodes and for providingother related functionality as taught herein. The other componentsillustrated in FIG. 2 are described below.

Sample operations of the system 100 and the femto node 200 will bedescribed in conjunction with the flowcharts of FIGS. 3-6, 9, 10, and12-13B. For convenience, the operations of FIGS. 3-6, 9, 10, and 12-13B(or any other operations discussed or taught herein) may be described asbeing performed by specific components (e.g., components of the femtonode 200). It should be appreciated, however, that these operations maybe performed by other types of components and may be performed using adifferent number of components. It also should be appreciated that oneor more of the operations described herein may not be employed in agiven implementation.

Referring initially to FIG. 3, the disclosure relates in some aspects todefining transmit power for a transmitter based on a maximum receivedsignal strength of a receiver and a minimum coupling loss between thetransmitter and a receiver. Here, an access terminal may be designed tooperate within a certain dynamic range where a lower limit is defined bya minimum performance specification. For example, a maximum receivedsignal strength (RX_MAX) of a receiver may be specified as −30 dBm.

For certain applications (e.g., employing femto nodes), an access nodeand its associated access terminal may be arbitrarily close to oneanother, thereby potentially creating relatively high signal levels atthe receiver. Assuming in one example a minimum separation of 20 cmbetween the femto node and an access terminal, the minimum path loss,also known as the minimum coupling loss (“MCL”), would be approximately28.5 dB. This MCL value is much smaller than typical MCL values observedin macro cell deployments (e.g., because the macro antennas aretypically installed on top of towers or buildings).

If the received power level exceeds the sensitivity range of a receiver,internal and external jammers and blockers of the receiver may sufferand, as a result, inter-modulation performance of the access terminalmay degrade. Moreover, if the received signal strength is very high(e.g., above 5 dBm) actual hardware damage may occur at the accessterminal. For example, an RF duplexer or a SAW filter may be permanentlydamaged in this case.

Accordingly, in some aspects the maximum transmit power (P_(MAX) _(_)_(HNB)) may be defined as: P_(MAX) _(_) _(HNB)<P_(HUE) _(_)_(MAX)=(MCL+RX_MAX). As an example, assuming MCL is 28.5 dB and Rx MAXis −30 dBm, the maximum power that may be transmitted to a home accessterminal (P_(HUE) _(_) _(MAX)) is: 28.5−30=−1.5 dBm. Therefore, P_(MAX)_(_) _(HNB)<−1.5 dBm in this example.

FIG. 3 illustrates several operations that may be performed to determinetransmit power based on the maximum received signal strength of areceiver and MCL. As represented by block 302, the femto node 200determines the maximum received signal strength (RX_MAX). In some casesthis value may simply be a design parameter that is predefined (e.g.,when the femto node 200 is provisioned). Thus, determining this valuemay simply involve retrieving a corresponding value 216 from the datamemory 212. In some cases, the maximum received signal strength may be aconfigurable parameter. For example, determining maximum received signalstrength may involve the node (e.g., the receiver 206) receiving anindication of the maximum received signal strength from another node(e.g., an access terminal).

As represented by block 304, the femto node 200 determines the minimumcoupling loss. In some cases this value may be a design parameter thatis predefined (e.g., when the femto node 200 is provisioned). Thus,determining the minimum coupling loss may involve retrieving acorresponding value 218 from the data memory 212. In some cases theminimum coupling loss may be a configurable parameter. For example,determining minimum coupling loss may involve the femto node 200 (e.g.,the receiver 206) receiving an indication of the minimum coupling lossfrom another node (e.g., an access terminal). In addition, in some casesdetermining minimum coupling loss may involve the node (e.g., acoupling/path loss determiner 220) calculating the minimum coupling loss(e.g., based on a received signal strength report received from anothernode such a home access terminal).

As represented by block 306, the femto node 200 (e.g., the transmitpower controller 208) determines the transmit power based on the maximumreceived signal strength and the minimum coupling loss. As discussedabove, this may involve defining a maximum transmit power to be lessthan the sum of these two parameters.

In some cases, the transmit power value determined at block 306 is butone of several maximum transmit power values determined by the femtonode 200. For example, the femto node 200 may employ other algorithms(e.g., as discussed below) to determine maximum transmit power values(e.g., TX_PWR_1 . . . TX_PWR_N) based on other criteria. The femto node200 may then select the lowest of these determined transmit power valuesas the actual “maximum” transmit power value. In some cases, thedetermination of this “maximum” transmit power value also may be subjectto constraints of a minimum transmit power value TX_MIN (e.g., to ensurethat the femto node 200 provides sufficient coverage for its home accessterminals) and an absolute maximum transmit power value TX_MAX. Asillustrated in FIG. 2, the above transmit power parameters 222 may bestored in the data memory 212.

As represented by block 308, the femto node 200 may then communicatewith another node or other nodes by transmitting signals constrainedaccording to the determined transmit power. For example, a femto nodemay limit its transmit power to remain below a determined maximum valueto avoid desensitizing any visiting access terminals that may come inclose proximity to the femto node.

Referring now to FIG. 4, the disclosure relates in some aspects todefining transmit power based on one or more channel conditions. As willbe discussed in more detail below, examples of such channel conditionsmay include total received signal strength, receive pilot strength, andchannel quality.

As represented by block 402, in some cases determination of transmitpower for an access node may be invoked due to or may be based on adetermination that a node is in a coverage area of the access node. Forexample, the femto node 200 may elect to recalibrate the femto'stransmit power (e.g., to increase the power) if it determines that ahome access terminal (e.g., a node that is authorized for data access)has entered the femto's coverage area. In addition, the femto node 200may elect to recalibrate its transmit power (e.g., to decrease thepower) if it determines that a visitor access terminal (e.g., that isnot authorized for data access) has entered its coverage area. To thisend, the femto node 200 may include a node detector 224 that maydetermine whether a particular type of node is in a given coverage area.

As represented by block 404, in the event the femto node 200 elects tocalibrate its transmitter (e.g., upon power-up, periodically, or inresponse a trigger such as block 402), the femto node 200 may determineone or more channel conditions. Such a channel condition may takevarious forms. For example, in some implementations a signal strengthdeterminer 226 may determine a total received signal strength value(e.g., a received signal strength indication, RSSI). In someimplementations a received pilot strength determiner 228 may determine asignal strength value associated with a pilot (e.g., received signalcode power, RSCP). Sample techniques relating to these channelconditions are described in more detail below in conjunction with FIGS.5 and 6.

In some implementations a channel quality determiner 230 may determine achannel quality (e.g., a channel quality indication, CQI). This channelquality may relate to, for example, the quality of a downlink channel ata home access terminal.

Various indications of channel quality may be employed in accordancewith the teachings herein. For example, channel quality may relate to asustainable data rate (e.g., data rate control, DRC), downlink qualityof service, signal-to-noise ratio (e.g., SINR where the noise mayinclude or substantially comprise interference), or some other qualitymetric. Channel quality also may be determined for various types ofchannels such as, for example, a data channel, a common control channel,an overhead channel, a paging channel, a pilot channel, or a broadcastchannel.

The channel quality determiner 230 may determine channel quality invarious ways. For example, in some implementations information relatingto channel quality may be received from another node (e.g., a homeaccess terminal). This information may take the form of, for example, anactual channel quality indication or information that may be used togenerate a channel quality indication.

As represented by block 406, the femto node 200 (e.g., the transmitpower controller 208) determines a transmit power value (e.g., a maximumvalue) based on the channel condition(s). For example, in animplementation where transmit power is based at least in part on achannel quality indication, the transmit power may be increased inresponse to a decrease in channel quality or if the channel qualityfalls below a threshold level. Conversely, the transmit power may bedecreased in response to an increase in channel quality or if thechannel quality rises above a threshold level. As a specific example, ifrequested DRC over a long time period is always very high, this mayserve an indication that the transmit power value may be to high and thefemto node 200 may therefore elect to operate at lower transmit powervalue.

As represented by block 408, the femto node 200 may determine one ormore other maximum transmit power values (e.g., based on the algorithmsdescribed herein or some other algorithm or criteria). The femto node200 may thus select the lowest of these determined transmit power values(e.g., TX_PWR_1 . . . TX_PWR_N stored in the data memory 212) as theactual “maximum” transmit power value as described above in conjunctionwith FIG. 3.

In some implementations the femto node 200 (e.g., the transmit powercontroller 208) may determine (e.g., adjust) the transmit power based onwhether there is a node in a coverage area of the femto node 200. Forexample, as discussed at block 402 transmit power may be decreased inthe presence of a visiting access terminal and transmit power may beincreased in the presence of a home access terminal.

As represented by block 410, the femto node 200 may communicate withanother node or other nodes by transmitting signals constrainedaccording to the determined transmit power. For example, if at somepoint in time the femto node 200 determines that interference with avisiting access terminal is unlikely, the femto node 200 may increaseits transmit power up to the lowest of the maximum values determined atblock 408.

As represented by block 412, in some implementations the femto node 200may repeatedly perform any of the above transmit power calibrationoperations (e.g., as opposed to simply determining the transmit power asingle time upon deployment). For example, the femto node 200 may use adefault transmit power value when it is first deployed and may thenperiodically calibrate the transmit power over time. In this case, thefemto node 200 may perform one or more of the operations of FIG. 4(e.g., acquire or receive signal strength or channel qualityinformation) at some other point(s) in time. In some cases, the transmitpower may be adjusted to maintain a desired channel quality over time(e.g., to maintain a minimum DRC value or minimum downlink quality ofservice value at a home access terminal). In some cases, the operationsmay be performed on a repeated basis (e.g., daily) so that a femto nodemay adapt to variations in the environment (e.g., a neighbor apartmentunit installs a new femto node). In some cases, such a calibrationoperation may be adapted to mitigate large and/or rapid changes intransmit power (e.g., through the use of a hysteresis or filteringtechnique).

Referring now to FIG. 5, techniques for determining transmit power basedon total received signal strength value and received pilot strength asmentioned above will now be treated in more detail. An access node suchas a femto node (e.g., femto node 200) operating within a macro cellenvironment may need to adjust downlink transmit power based on itslocation within a macro cell. When the femto node is located at the edgeof the macro cell, RF leakage outside of the femto node environment(e.g., a residence) may significantly reduce Ec/Io of nearby macroaccess terminals since the macro signal levels are typically very smallin these cell edge locations. As a result, there may be a relative largecoverage hole for macro access terminals in the vicinity of the femtonode.

If macro access terminals that are not associated with the femto node(e.g., visitor access terminal) enter the coverage region of the femtonode, the macro cell network may perform inter-frequency handovers todirect the visitor access terminals to another carrier frequency.Although this technique may reduce the likelihood of call drop orservice outage for macro access terminals, it also may result infrequent inter-frequency handoff events for mobile macro accessterminals passing through the coverage holes which, in turn, may causeservice interruptions and high signaling load on macro cell accessnodes. Thus, in some aspects it may be desirable to minimize the size ofcoverage hole created by the femto node on the macro cell.

On the other hand, if the transmit power level of the femto node is settoo low, then proper femto coverage may not be maintained within thefemto environment. Moreover, the desired transmit power level may dependon where the femto node is located. For example when a femto node isclose to a macro access node, larger transmit power levels may berequired to provide adequate femto coverage as compared to when a femtonode is located at the edge of a macro cell. Also, different powerlevels may be specified in urban environments (e.g., where femto nodesmay be often be deployed in apartments) than are specified in less densesuburban environments.

The disclosure relates in some aspect to adaptively adjusting the femtonode transmit power level through the use of macro cell signal values tolimit interference at a visitor access terminal. These operations may beemployed to accommodate a visitor access terminal that is operating onan adjacent channel relative to the femto node or on a co-channel withthe femto node.

Briefly, the operations of FIG. 5 involve determining the maximumallowed interference that a femto node can create at a visitor accessterminal located at an edge of a coverage hole. Here, the maximumallowed interference may be defined as the minimum required Ecp/Io(e.g., received pilot strength over total received signal strength) forreliable macro downlink operation at the visitor access terminal on agiven channel. The maximum allowed interference may be derived from themeasured received pilot signal strength (Ecp) from the best macro cellon the carrier, the measured total signal strength (Io) on the carrier,and the minimum required Ecp/Io. The maximum transmit power for thefemto may then be derived based on the maximum allowed interference andthe path loss between the femto node and the edge of the coverage hole(and the adjacent channel interference rejection, if applicable).

For a predetermined downlink transmit power P_(HNB) of a femto node(e.g., home NodeB, HNB) and a corresponding adjacent carrierinterference ratio (“ACIR”) of, for example, 33 dB at a distance “d”from the femto node, a visitor access terminal (e.g., user equipment,UE) may experience interference from the femto node as high as:Rx _(VUE)(d)=P _(HNB)−ACIR−PL_(FREE)(d)  EQUATION 1

where PL_(FREE)(d) is the free path loss between the transmitter and thereceiver equipment separated by a distance “d,” and that may becalculated with the formula:PL_(FREE)(d)=20 log₁₀(4πdf/c)−G _(T) −G _(R)  EQUATION 2

where f is the carrier frequency (e.g., f=2 GHz), and G_(T) and G_(R)are respective transmitter and receiver antenna gains (e.g.,G_(T)=G_(R)=−2 dB).

To limit the interference on the visitor access terminal, the femto nodeadjusts the downlink transmit power P_(HNB) by measuring the macrosignal strength, as described in further detail below. In someimplementations, the femto node measures the following quantities in anadjacent channel (e.g., the algorithm is run separately on multipleadjacent carriers) or a co-channel:

-   -   RSCP_(BEST) _(_) _(MACRO) _(_) _(AC)=A received pilot signal        strength value from the best macro cell in the adjacent carrier.    -   RSSI_(MACRO AC)=Total interference signal strength value (Io) in        the adjacent carrier.

Accordingly, as represented by block 502 in FIG. 5, the femto node 200of FIG. 2 (e.g., the signal strength determiner 226) determines thetotal received signal strength (e.g., RSSI) on the visitor accessterminal's channel. The signal strength determiner 226 may determine thesignal strength in various ways. For example, in some implementationsthe femto node 200 measures the signal strength (e.g., the receiver 206monitors the appropriate channel). In some implementations informationrelating to the signal strength may be received from another node (e.g.,a home access terminal). This information may take the form of, forexample, an actual signal strength measurement (e.g., from a node thatmeasured the signal strength) or information that may be used todetermine a signal strength value.

Also, as represented by block 504, the femto node 200 (e.g., thereceived pilot strength determiner 228) determines the received pilotstrength (e.g., RSCP) of the best macro access node on the visitoraccess terminal's channel. In other words, the signal strength of thepilot signal having the highest received signal strength is determinedat block 504. The received pilot strength determiner 228 may determinethe received pilot strength in various ways. For example, in someimplementations the femto node 200 measures the pilot strength (e.g.,the receiver 206 monitors the appropriate channel). In someimplementations information relating to the pilot strength may bereceived from another node (e.g., a home access terminal). Thisinformation may take the form of, for example, an actual pilot strengthmeasurement (e.g., from a node that measured the signal strength) orinformation that may be used to determine a pilot strength value.

In some implementations, the received pilot strength may be determined(e.g., estimated) from the total received signal strength obtained atblock 502. This determination may be based on, for example, a known orestimated relationship between the pilot strength and the total strengththat is embodied in the form of information 232 (e.g., a function, atable, or a graph) stored in the data memory 212. In such animplementation, the signal strength determiner 226 may comprise thereceived signal strength determiner 228.

As represented by block 506, the femto node 200 (e.g., the path/couplingloss determiner 220) determines the path loss between the femto node anda given location (e.g., an edge of a coverage hole or a location of anode) on the visitor access terminal's channel. The path/coupling lossdeterminer 220 may determine the path loss in various ways. In somecases the path loss may simply be a design parameter that is predefined(e.g., when the femto node 200 is provisioned) such that the path lossvalue corresponds to a coverage hole of a given size. Thus, determiningthe path loss may simply involve retrieving a corresponding value 218from the data memory 212. In some cases, determining path loss mayinvolve the node (e.g., the receiver 206) receiving an indication of thepath loss from another node (e.g., an access terminal). In addition, insome cases determining path loss may involve the femto node 200 (e.g.,the path/coupling loss determiner 220) calculating the path loss. Forexample path loss may be determined based on a receive signal strengthreport received from another node such as a home access terminal. As aspecific example, the path loss to an edge of a femto node's coverageboundary may be determined based on the last measurement report (e.g.,reporting the strength of a signal received from the femto node)received from a home access terminal before it performs a handoff toanother access node. Here, an assumption may be made that the accessterminal may be near the boundary since the access terminal is doing ahandoff. In some cases, the femto node 200 may determine multiple passloss values over time and generate a final path loss value based on thecollected path loss values (e.g., set the path loss to the maximumvalue).

As represented by block 508, the femto node 200 (e.g., an errordeterminer 234) may optionally determine one or more error valuesrelating to the determination of the total received signal strengthand/or the received pilot strength. For example, the error determiner234 may receive total received signal strength and received pilotstrength information from a node (e.g., a home access terminal) thatmeasured these values at various locations in or near the coverage areaof the femto node 200. The error determiner 234 may then compare thesevalues with corresponding values measured at the femto node 200. Errorvalues may then be determined based on the difference betweencorresponding sets of these values. In some cases, this operation mayinvolve collecting error information over time, and defining errorvalues based on the collected information (e.g., based on the range ofthe collected error information). Error information 236 corresponding tothe above may be stored in the data memory 212.

As represented by block 510, the femto node 200 (e.g., an interferencedeterminer 238) determines the maximum allowed interference based on thetotal received signal strength, the received pilot strength, and theminimum required Ecp/Io for a visitor access terminal (e.g., apilot-to-signal ratio).

In WCDMA and 1×RTT systems, pilot and control channels are code divisionmultiplexed with traffic and are not transmitted at full power (e.g.,Ecp/Io<1.0). Thus, when the femto node performs the measurements, ifneighboring macro cells are not loaded, the total interference signalstrength value RSSI_(MACRO) _(_) _(AC) may be lower than a correspondingvalue for a case wherein the neighboring macro cells are loaded. In oneexample, considering a worst case scenario, the femto node may estimatesystem loading and adjust the RSSI_(MACRO) _(_) _(AC) value to predictthe value for a fully loaded system.

Ecp/Io (P-CPICH Ec/No in 3GPP terminology) experienced by the visitoraccess terminal may be calculated as follows:(Ecp/Io)_(LINEAR)=RSCP_(BEST) _(_) _(MACRO) _(_) _(AC) _(_)_(LINEAR)/(RSSI_(MACRO) _(_) _(AC) _(_) _(LINEAR) +I _(HNB) _(_)_(LINEAR))   EQUATION 3

where all the quantities have linear units (instead of dB) and I_(HNB)_(—LINEAR) corresponds to interference created by the femto node at thevisitor access terminal.

If, as an example, a minimum required value for (Ecp/Io)_(LINEAR) toensure a reliable down link operation is (Ecp/Io)_(MIN) _(_) _(LINEAR),then the femto node computes a parameter indicative of the maximumallowed interference that it can induce at the visitor access terminal,such that the resultant value at the minimum distance is equal to(Ecp/Io)_(MIN), as follows:

$\begin{matrix}{I_{{HNB\_ MAX}{\_ ALLOWED}{\_ LINEAR}} = {{\frac{R\; S\; C\; P_{{BEST\_ MACRO}{\_ AC}{\_ LINEAR}}}{\left( {{Ecp}/{Io}} \right)_{MIN\_ LINEAR}} - {R\; S\; S\; I_{{MACRO\_ AC}{\_ LINEAR}}}} = \mspace{25mu}{R\; S\; S\;{I_{{MACRO\_ AC}{\_ LINEAR}}\left( {\frac{\left( {{Ecp}/{Io}} \right)_{{MACRO\_ AC}{\_ LINEAR}}}{\left( {{Ecp}/{Io}} \right)_{MIN\_ LINEAR}} - 1} \right)}}}} & {{EQUATION}\mspace{14mu} 4}\end{matrix}$

As represented by block 512 of FIG. 5, the femto node 200 (e.g., thetransmit power controller 208) determines the maximum transmit powerbased on the allowed interference, the path loss and, optionally, theACIR for the femto node 200. As mentioned above, the operations of FIG.5 may be used for limiting the coverage hole on either an adjacentchannel or a co-channel. In the former case ACIR may be a predefinedvalue (e.g., dependent on the design parameters of the system). In thelatter case, ACIR is 0 dB. An ACIR value 240 may be stored in the datamemory 212.

In some aspects, a femto node may thus convert the calculated maximumallowed interference value at an actual or hypothetical visitor accessterminal to a corresponding allowed transmit power value, such that at apredetermined minimum distance I_(HNB) _(_) _(MAX) _(_) _(ALLOWED) isachieved. For example, if the allowed coverage hole radius around thefemto node is d_(HNB) _(_) _(AC) _(_) _(COVERAGE) _(_) _(HOLE), then thecorresponding path loss value PL can be calculated with the aboveformula, i.e., PL_(FREE) _(_) _(SPACE) (d_(HNB) _(_) _(AC) _(_)_(COVERAGE) _(_) _(HOLE)), and:P _(MAX) _(_) _(HNB) <P _(VUE) _(_) _(AC) _(_) _(MAX)=(I _(HNB) _(_)_(MAX) _(_) _(ALLOWED)+PL_(FREE) _(_) _(SPACE)(d _(HNB) _(_) _(AC) _(_)_(COVERAGE) _(_) _(HOLE))+ACIR)  EQUATION 5The transmit power may thus be defined in a manner that enablesoperation of a visiting access terminal at a predetermined minimumdistance from a femto node (e.g., corresponding to an edge of a coveragehole), without unduly restricting the operation of the femto node's homeaccess terminals. Consequently, it may be possible for both the visitingand home access terminals to operate effectively near the edge of thecoverage hole.

With the above in mind, additional considerations relating to scenarioswhere a macro access terminal (e.g., a visitor access terminal) that isnot associated with a femto node is at or near a coverage area of thefemto node will now be treated. Here, a femto node (e.g., located near awindow) may jam macro access terminals passing by (e.g., on a street) ifthese macro access terminals are not be able to handoff to the femtonode due to a restricted association requirement. The followingparameters will be used in the discussion:

-   -   Ecp_(MNB) _(_) _(UE): Received pilot strength (RSCP) from the        best macro access node (e.g., MNB) by the macro access terminal        (e.g., UE) (in linear units).    -   Ecp_(MNB) _(_) _(HNB): Received pilot strength (RSCP) from best        macro access node by the femto node (e.g., HNB) (in linear        units).    -   Ec_(HNB) _(_) _(UE): Total received signal strength (RSSI) from        the femto node by the macro access terminal (in linear units).        (Also known as RSSI_(MNB) _(_) _(UE)).    -   Ec_(HNB) _(_) _(HNB): Total received signal strength (RSSI) from        the femto node by the macro access terminal (in linear units).        (Also known as RSSI_(MNB) _(_) _(HNB)).

As the macro access terminal gets close to the coverage of the femtonode, the desired behavior is for the macro cell to move the accessterminal to another carrier as discussed above. In CDMA systems, thistrigger is based on the Ecp_(HNB) _(_) _(UE)/Io value going above acertain T_ADD threshold value. In one example, in 1×EV-DO, theinterfrequency handoff trigger would be: Ecp_(HNB) _(_) _(UE)/Io>T_ADD,where an example value for T_ADD=−7 dB (T_ADD_(LINEAR)=0.2). On theother hand, in WCDMA systems, relative signal strength with respect tothe best macro cell is typically used as the trigger. For example, whenEcp_(HNB) _(_) _(UE) gets within a certain range of Ecp_(MNB) _(_)_(UE): Ecp_(MNB) _(_) _(UE)−Ecp_(HNB) _(_) _(UE)=Δ_(HO) _(_)_(BOUNDARY), and Δ_(HO) _(_) _(BOUNDARY) may take values around, forexample, 4 dB, but the 3GPP standard allows for each individual cell tohave a different offset.

In some cases, if the macro access terminal that experiences a certainEcp_(MNB) _(_) _(UE)/Io value approaches a femto node which is fullyloaded (i.e., 100% transmit power), then one question is whetherEcp_(MNB) _(_) _(UE)/Io will degrade below a certain minimum threshold(e.g., Ec/Io_min=−16 dB) until it is directed to another carrier. LetRSSI_(MACRO) indicate the total received signal strength (e.g., 10) bythe macro access terminal, excluding the interference from the femtonode. Then, at the handoff boundary:

$\begin{matrix}{{{Ecp}_{MNB\_ UE}/{Io}} = \frac{{{Ecp}_{MNB\_ UE}/R}\; S\; S\; I_{MACRO}}{1 + \left( {{\alpha \cdot {{Ecp}_{HNB\_ UE}/R}}\; S\; S\; I_{MACRO}} \right)}} & {{EQUATION}\mspace{14mu} 6}\end{matrix}$

where α corresponds to the total femto node transmit power value dividedby the pilot power value (i.e., Ior/Ecp).

For 1×EV-DO systems, for example:

$\begin{matrix}{{{{Ecp}_{HNB\_ UE}/R}\; S\; S\; I_{MACRO}} = \frac{{T\_ ADD}_{LINEAR}}{\left( {1 - {T\_ ADD}_{LINEAR}} \right)}} & {{EQUATION}\mspace{14mu} 7}\end{matrix}$

and for example values T_ADD=−7 dB and α=1:

$\begin{matrix}{{{{Ecp}_{MNB\_ UE}/{Io}}❘_{{1{xEV}} - {DO}}} = \frac{{{Ecp}_{MNB\_ UE}/R}\; S\; S\; I_{MACRO}}{1.25}} & {{EQUATION}\mspace{14mu} 8}\end{matrix}$

In another example, for WCDMA, assuming Δ_(HO) _(_) _(BOUNDARY)=4 dB andα=10:

$\begin{matrix}{{{{Ecp}_{MNB\_ UE}/{Io}}❘_{WCDMA}} = \frac{{{Ecp}_{MNB\_ UE}/R}\; S\; S\; I_{MACRO}}{1 + {4\left( {{{Ecp}_{HNB\_ UE}/R}\; S\; S\; I_{MACRO}} \right)}}} & {{EQUATION}\mspace{14mu} 9}\end{matrix}$

As described above, for an interfrequency handoff-based mechanism, therelative degradation of a macro access terminal at the handoff boundarymay be tolerable. Next, the distance of this interfrequency handoffboundary from the edge of the femto node is addressed. In some aspects,if this distance is very large, the utilization of the same carrier bythe macro access terminal may be very small (especially if there are alarge number of femto cells in a macro cell). In other words, theinterfrequency handoff mechanism may work well (independent of the femtonode downlink transmit power) and macro access terminals may operatereliably outside femto node handoff boundaries. However, if large femtonode transmit power values are used, the handoff boundaries extendtowards the macro cell and the regions where co-channel macro accessterminals operate effectively may be very limited. In the exampledescribed above, it is assumed that the home node may effectivelymeasure Ecp and RSSI values experienced by the visitor access terminalbecause the visitor access terminal is assumed to be very close to thefemto node at a predetermined distance (e.g., a few meters). However,when the macro access terminal is outside the femto residence, Ecp_(MNB)_(_) _(UE) and Ecp_(MNB) _(_) _(HNB) may take different values. Forexample, Ecp_(MNB) _(_) _(HNB) may experience penetration loss, whileEcp_(MNB) _(_) _(UE) may not. This may lead to the conclusion thatEcp_(MNB) _(_) _(UE) is always greater than Ecp_(MNB) _(_) _(HNB).However, sometimes the femto node residence creates a shadow effectwhereby Ecp_(MNB) _(_) _(UE) is lower than Ecp_(MNB) _(_) _(HNB) (e.g.,the femto node is located between a macro access node and a macro accessterminal). In one example, the difference between the femto node bestmacro Ecp measurement and macro access terminal best macro Ecpmeasurement at the handoff boundary is:Δ_(Ecp) _(_) _(MEAS) _(_) _(DIFF) _(_) _(HO) _(_) _(BOUNDARY) =Ecp_(MNB) _(_) _(UE) −Ecp _(MNB) _(_) _(HNB)  EQUATION 10

Similarly, the difference between macro RSSI measurements at the femtonode and the macro access terminal at the handoff boundary may becalculated as follows:Δ_(RSSI) _(_) _(MEAS) _(_) _(DIFF) _(_) _(HO) _(_)_(BOUNDARY)=RSSI_(MNB) _(_) _(UE)−RSSI_(MNB) _(_) _(HNB)  EQUATION 11

In some aspects, these values may comprise the error informationdescribed above at block 508.

Based on prior measurements, a range of values could be applied forΔ_(Ecp) _(_) _(MEAS) _(_) _(DIFF) _(_) _(HO) _(_) _(BOUNDARY). Then, inone example, the downlink transmit power (P_(HNB)) of the femto node maybe decided based on constraints described in detail above (e.g.,Equations 4 and 5), wherein, for example, ACIR=0 dB, since, in thiscase, the access terminal is not on an adjacent channel, but it is on aco-channel with the femto node, and wherein PL_(FREE) _(_)_(SPACE)(d_(HNB) _(_) _(AC) _(_) _(COVERAGE) _(_) _(HOLE)) is replacedby a desired path loss value to the co-channel coverage hole.

In some cases, a femto node may be located next to an external wall orwindow of a residence. This femto node may create a maximum amount ofinterference to the macro cell on the outside of the wall/window. If theattenuation due to the wall/window is PL_(WALL) and, in one example, forsimplicity Δ_(HNB) _(_) _(MUE) _(_) _(MEAS) _(_) _(DIFF)=0 dB andΔ_(RSSI) _(_) _(MNB) _(_) _(MUE) _(_) _(MEAS) _(_) _(DIFF)=0 dB, then:Ecp_(HNB UE)(d)=(Ecp/Ior)P_(HNB)−PL_(FREE)(d)−PL_(WALL), where the totalfemto node downlink transmit power (P_(HNB)) is decided based on theconstraints described above.

One method to reduce the coverage holes created by the femto node is toreduce Ecp/Ior for the femto node. However, it may not be desirable toreduce the femto node Ecp/Ior arbitrarily since this may bring thehandoff boundary closer to the femto node and macro access terminalperformance may degrade significantly if the femto node is loaded.Moreover, a predetermined minimum Ecp level may be defined forsuccessful operation of access terminals in the femto coverage (e.g.,channel estimation, etc.) to allow them to hand in to the femto coveragefrom macro cell coverage. Thus, in some cases a hybrid method may beimplemented such that when there is no active user served by the femtonode, Ecp/Ior may be reduced to a reasonably low value, such that, forthose periods of time, the coverage hole in the macro cell is limited.In other words, the transmit power may be adjusted based on whether anode is in the vicinity of the femto node as discussed above at block408.

For a home access terminal, Ecp may be calculated as follows:Edp_(HUE)=P_(HNB)−Ecp/Ior−PL_(HNB), where PL_(HUE) corresponds to thepath loss from the femto node to the home access terminal.

In some cases, there is no interference from neighboring accessterminals and all interference is coming from the macro cell and thethermal noise floor. One of the important parameters in the aboveequation is PL_(HUE). A common model used for indoor propagation is:

$\begin{matrix}{{{PL}_{HNB}(d)} = {{20{\log\left( \frac{4\pi\; f}{c} \right)}} + {20{\log(d)}} + {\sum\limits_{i}W_{i}}}} & {{EQUATION}\mspace{14mu} 12}\end{matrix}$

where W_(i); is the penetration loss through internal walls.

Referring now to FIG. 6, in some implementations the maximum transmitpower defined by the femto node 200 may be constrained based on asignal-to-noise ratio for a home access terminal located around the edgeof a coverage hole. For example, if the signal-to-noise ratio is higherthan expected at a home access terminal that is located where thecoverage hole is expected to end, this means that the coverage hole mayin fact be much larger than desired. As a result, undue interference maybe imposed on visitor access terminals near the intended coverage edge.

The disclosure relates in some aspects to reducing the transmit power ifthe signal-to-noise ratio at the home access terminal is higher thanexpected. The following parameters are used in the discussion thatfollows:

-   -   Io_(UE): Total received signal strength (Io) by the home access        terminal (e.g., UE) from all access nodes (e.g., NodeBs) in the        absence of the femto node (in linear units).    -   Io_(HNB): Total received signal strength (Io) by the home access        terminal from all other access nodes (e.g., macro and femto        access nodes) in the system (in linear units).    -   PL_(HNB) _(_) _(edge): Path loss from the femto node (e.g., HNB)        to the home access terminal at the coverage edge (in dB units).

When a femto node is not transmitting, received Ecp/Io by a macro accessterminal may be:

$\begin{matrix}{{{{Ecp}/{Io}}❘_{{HNB\_ not}{\_ transmitting}}} = \frac{{Ecp}_{MNB\_ UE}}{{Io}_{UE}}} & {{EQUATION}\mspace{14mu} 13}\end{matrix}$

When the femto node is transmitting, received Ecp/Io by the accessterminal may be:

$\begin{matrix}{{{{Ecp}/{Io}}❘_{HNB\_ transmitting}} = \frac{{Ecp}_{MNB\_ UE}}{{Io}_{UE} + {Ec}_{HNB\_ UE}}} & {{EQUATION}\mspace{14mu} 14}\end{matrix}$

The parameter [Ecp/Io]_(min) is defined as the minimum required Ecp/Iofor the macro access terminal to have proper service (e.g., as discussedabove at FIG. 5). Assuming the macro access terminal is at the edge of afemto node coverage hole and the coverage hole is limited to a certainvalue (e.g., PL_(HNB) _(_) _(edge)=80 dB), then one may impose thefollowing condition for the femto node downlink maximum transmit power:P_(HNB) _(_) _(max) (e.g., to maintain [Ecp/Io]_(min) for a macro accessterminal):

$\begin{matrix}{P_{HNB\_ max} < {\left\lbrack {\left( \frac{{Ecp}_{MNB\_ UE}}{\left\lbrack {{Ecp}/{Io}} \right\rbrack_{\min}} \right) - {Io}_{UE}} \right\rbrack \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 15}\end{matrix}$

Similarly, if a home access terminal (e.g., a home UE, HUE) that isserviced by the femto node is located at the edge of the femto coverage,the SNR (the term SINR, e.g., including interference, will be used inthe following discussion) experienced by the home access terminal may bedescribed as:

$\begin{matrix}{{SINR}_{HUE} = \frac{P_{HNB\_ max}}{{Io}_{UE} \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 16}\end{matrix}$

In some cases Equation 16 may yield to relatively large transmit powerlevels for the femto node which may result in unnecessarily highSINR_(HUE). This may mean, for example, that if a new femto node isinstalled in the vicinity of the old femto node, the new femto node mayend up receiving a high level of interference from the previouslyinstalled femto node. As a result, the newly installed femto node may beconfined to a lower transmit power level and may not provide sufficientSINR for its home access terminals. To prevent this type of effect anSINR cap may be used for the home access terminal at the edge of itshome access terminal coverage as: [SINR]_(max) _(_) _(at) _(_) _(HNB)_(_) _(edge). Thus, one may provide a second constraint for the P_(HNB)_(_) _(max) as:

$\begin{matrix}{P_{HNB\_ max} < {\lbrack{SNR}\rbrack_{{max\_ at}{\_ HBN}{\_ edge}} \cdot {Io}_{UE} \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 17}\end{matrix}$

To apply constraints as described in Equations 15 and 17 one may measureEcp_(MNB) _(_) _(UE) and Io_(UE) at the edge of desired HNB coverage(PL_(HNB) _(_) _(edge)).

Since professional installation may not be practical for femto nodes(e.g., due to financial constraints), a femto node may estimate thesequantities by its own measurements of the downlink channel. For example,the femto node may make measurements: Ecp_(MNB) _(_) _(HNB) and Io_(HNB)to estimate Ecp_(MNB) _(_) _(UE) and Io_(UE) respectively. This scenariois discussed in more detail below in conjunction with Equation 19. Sincethe femto node location is different than the access terminal locationthere may be some error in these measurements.

If the femto node uses its own measurements for adaptation of its owntransmit power, this error could result in lower or higher transmitpower values compared to optimum. As a practical method to prevent worstcases errors, certain upper and lower limits may be enforced on P_(HNB)_(_) _(max) as P_(HNB) _(_) _(max) limit and P_(HNB) _(_) _(min) _(_)_(limit) (e.g., as discussed above).

In view of the above, referring to block 602 FIG. 6, a transmit poweradjustment algorithm may thus involve identifying a home access terminalnear a coverage edge of a femto node. In the example of FIG. 2, thisoperation may be performed by the node detector 224. In someimplementations, the position of the home access terminal may bedetermined based on path loss measurements between the home accessterminal and the femto node (e.g., as discussed herein).

At block 604, the femto node 200 (e.g., an SNR determiner 242) maydetermine SNR values (e.g., SINR) associated with the home accessterminal. In some cases, this may involve receiving SNR information fromthe home access terminal (e.g., in a channel quality report or ameasurement report). For example, the home access terminal may sendmeasured RSSI information or calculated SNR information to the femtonode 200. In some cases, CQI information provided by the home accessterminal may be correlated (e.g., by a known relationship) to an SNRvalue of the home access terminal. Thus, the femto node 200 may deriveSNR from received channel quality information.

As mentioned above, determining an SNR value may involve the femto node200 autonomously calculating the SNR value as discussed herein. Forexample, in cases where the femto node 200 performs the measurementoperations on its own, the femto node 200 may initially measure:

-   -   Ecp_(MNB) _(_) _(HNB): Total received pilot strength from best        macro access node by the femto node.    -   Io_(HNB): Total received signal strength (Io) by the femto node        from all other access nodes (e.g., macro and femto nodes) in the        system.

The femto node 200 may then determine upper power limits:

$\begin{matrix}{P_{{HNB\_ max}\_ 1} = {\left\lbrack {\left( \frac{{Ecp}_{MNB\_ HNB}}{\left\lbrack {{Ecp}/{Io}} \right\rbrack_{\min}} \right) - {Io}_{HNB}} \right\rbrack \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 18} \\{P_{{HNB\_ max}\_ 2} = {\lbrack{SINR}\rbrack_{{max\_ at}{\_ HNB}{\_ edge}} \cdot {Io}_{HNB} \cdot 10^{({{PL}_{HNB\_ edge}/10})}}} & {{EQUATION}\mspace{14mu} 19}\end{matrix}$

Here, Equation 18 relates to the maximum transmit power determined in asimilar manner as discussed in FIG. 5 and Equation 19 relates todetermining another maximum limit for the transmit power based on SNR.It may be observed that Equation 18 is similar to Equation 17 exceptthat Io is measured at the femto node. Thus, Equation 18 also providesthe constraint that the SNR at the node not be greater than or equal toa defined maximum value (e.g., a SNR value 244 stored in data memory212). In both of these equations, the determined transmit power is basedon signals received at the femto node and on the path loss to thecoverage edge (e.g., based on the distance to the edge).

At block 606 of FIG. 6, the femto node 200 (e.g., the transmit powercontroller 208) may determine the transmit power based on the maximumsdefined by Equations 18 and 19. In addition, as mentioned above thefinal maximum power value may be constrained by absolute minimum andmaximum values:P _(HNB) _(_) _(total)=max └P _(HNB) _(_) _(min) _(_) _(limit),min(P_(HNB) _(_) _(max1) ,P _(HNB) _(_) _(max2) ,P _(HNB) _(_) _(max) _(_)_(limit))┘  EQUATION 20

As an example of Equation 20, PL_(HNB) _(_) _(edge) may be specified tobe 80 dB, P_(HNB) _(_) _(max) _(_) _(limit) may be specified to be 20dBm, P_(HNB) _(_) _(min) _(_) _(limit) may be specified to be −10 dBm,and [SINR]_(max) _(_) _(at) _(_) _(HNB) _(_) _(edge) and [Ecp/Io]_(min)may depend on the particular air interface technology in use.

As mentioned above, the teachings herein may be implemented in awireless network that includes macro coverage areas and femto coverageareas. FIG. 7 illustrates an example of a coverage map 700 for a networkwhere several tracking areas 702 (or routing areas or location areas)are defined. Specifically, areas of coverage associated with trackingareas 702A, 702B, and 702C are delineated by the wide lines in FIG. 7.

The system provides wireless communication via multiple cells 704(represented by the hexagons), such as, for example, macro cells 704Aand 704B, with each cell being serviced by a corresponding access node706 (e.g., access nodes 706A-706C). As shown in FIG. 7, access terminals708 (e.g., access terminals 708A and 708B) may be dispersed at variouslocations throughout the network at a given point in time. Each accessterminal 708 may communicate with one or more access nodes 706 on aforward link (“FL”) and/or a reverse link (“RL) at a given moment,depending upon whether the access terminal 708 is active and whether itis in soft handoff, for example. The network may provide service over alarge geographic region. For example, the macro cells 704 may coverseveral blocks in a neighborhood. To reduce the complexity of FIG. 7,only a few access nodes, access terminals, and femto nodes are shown.

The tracking areas 702 also include femto coverage areas 710. In thisexample, each of the femto coverage areas 710 (e.g., femto coverage area710A) is depicted within a macro coverage area 704 (e.g., macro coveragearea 704B). It should be appreciated, however, that a femto coveragearea 710 may not lie entirely within a macro coverage area 704. Inpractice, a large number of femto coverage areas 710 may be defined witha given tracking area 702 or macro coverage area 704. Also, one or morepico coverage areas (not shown) may be defined within a given trackingarea 702 or macro coverage area 704. To reduce the complexity of FIG. 7,only a few access nodes 706, access terminals 708, and femto nodes 710are shown.

FIG. 8 illustrates a network 800 where femto nodes 802 are deployed inan apartment building. Specifically, a femto node 802A is deployed inapartment 1 and a femto node 802B is deployed in apartment 2 in thisexample. The femto node 802A is the home femto for an access terminal804A. The femto node 802B is the home femto for an access terminal 804B.

As illustrated in FIG. 8, for the case where the femto nodes 802A and802B are restricted, each access terminal 804 may only be served by itsassociated (e.g., home) femto node 802. In some cases, however,restricted association may result in negative geometry situations andoutages of femto nodes. For example, in FIG. 8 the femto node 802A iscloser to the access terminal 804B than the femto node 802B and maytherefore provide a stronger signal at the access terminal 804B. As aresult, the femto node 802A may unduly interfere with reception at theaccess terminal 804B. Such a situation may thus affect the coverageradius around the femto node 802B at which an associated access terminal804 may initially acquire the system and remain connected to the system.

Referring now to FIGS. 9-13B, the disclosure relates in some aspects toadaptively adjusting transmit power (e.g., maximum downlink transmitpower) of neighboring access nodes to mitigate scenarios of negativegeometries. For example, as mentioned above maximum transmit power maybe defined for overhead channels that are then transmitted as theirdefault fraction of the maximum access node transmit power. Forillustration purposes, the following describes a scenario where transmitpower of a femto node is controlled based on a measurement reportgenerated by an access terminal associated with a neighboring femtonode. It should be appreciated, however, that the teachings herein maybe applied to other types of nodes.

Transmit power control as taught herein may be implemented through adistributed power control scheme implemented at the femto nodes and/orthrough the use of a centralized power controller. In the former case,adjustments of transmit power may be accomplished through the use ofsignaling between neighboring femto nodes (e.g., femto nodes associatedwith the same operator). Such signaling may be accomplished, forexample, through the use of upper layer signaling (e.g., via thebackhaul) or appropriate radio components. In the latter case mentionedabove, adjustments to transmit power of a given femto node may beaccomplished via signaling between femto nodes and a centralized powercontroller.

The femto nodes and/or the centralized power controller may utilizemeasurements reported by access terminals and evaluate one or morecoverage criteria to determine whether to send a request to a femto nodeto reduce transmit power. A femto node that receives such a request mayrespond by lowering its transmit power if it is able to maintain itscoverage radius and if its associated access terminals would remain ingood geometry conditions.

FIG. 9 describes several operations relating to an implementation whereneighboring femto nodes may cooperate to control one another's transmitpower. Here, various criteria may be employed to determine whethertransmit power of a neighbor node should be adjusted. For example, insome aspects a power control algorithm may attempt to maintain aparticular coverage radius around the femto node (e.g., a certain CPICHEcp/Io is maintained a certain path loss away from the femto node). Insome aspects a power control algorithm may attempt to maintain a certainquality of service (e.g., throughput) at an access terminal. Initially,the operations of FIGS. 9 and 10 will be described in the context of theformer algorithm. The operations of FIGS. 9 and 10 will then bedescribed in more detail in the context of the latter algorithm as well.

As represented by block 902 of FIG. 9, a given femto node initially setits transmit power to defined value. For example, all of the femto nodesin the system may initially set their respective transmit power to themaximum transmit power that still mitigates the introduction of coverageholes in a macro coverage area. As a specific example, the transmitpower for a femto node may be set so that the CPICH Ecp/Io of a macroaccess terminal at a certain path loss away (e.g. 80 dB) from the femtonode is above a certain threshold (e.g. −18 dB). In someimplementations, the femto nodes may employ one or more of thealgorithms described above in conjunction with FIGS. 2-6 to establish amaximum transmit power value.

As represented by block 904, each access terminal in the network (e.g.,each access terminal associated with a femto node) may measure thesignal strength of signals that it receives in its operating band. Eachaccess terminal may then generate a neighbor report including, forexample, the CPICH RSCP (pilot strength) of its femto node, the CPICHRSCP of all femto nodes in its neighbor list, and the RSSI of theoperating band.

In some aspects, each access terminal may perform this operation inresponse to a request from its home femto node. For example, a givenfemto node may maintain a list of neighboring femto nodes that it sendsto its home access terminals. This neighbor list may be supplied to thefemto node by an upper layer process or the femto node may populate thelist on its own by monitoring downlink traffic (provided the femto nodeincludes appropriate circuitry to do so). The femto node may repeatedly(e.g., periodically) send a request to its home access terminals for theneighbor report.

As represented by blocks 906 and 908, the femto node (e.g., the transmitpower controller 208 of FIG. 2) determines whether signal reception ateach of its home access terminals is acceptable. For example, for animplementation that seeks to maintain a particular coverage radius, agiven femto node “i” (e.g., home Node B, “HNB”) may estimate the CPICHEcp/Io_i of a given associated access terminal “i” (e.g., home userequipment, “HUE”) assuming the access terminal “i” is a certain pathloss (PL) away from the femto node “i” (e.g., assuming the locationmeasured by the femto node “i” will not change much). Here Ecp/Io_i forthe access terminal “i” is

${{Ecp}/{Io\_ i}} = {\frac{{Ecp}_{{HNB\_ HUE}{\_ i}}}{{Io}_{HUE\_ i}}.}$

In some implementations, a femto node (e.g., the signal strengthdeterminer 226) may determine RSSI on behalf of its home accessterminals. For example, the femto node may determine RSSI for an accessterminal based on the RSCP values reported by an access terminal. Insuch a case, the access terminal need not send an RSSI value in theneighbor report. In some implementations, a femto node may determine(e.g., estimate) RSSI and/or RSCP on behalf of its home accessterminals. For example, the signal strength determiner 226 may measureRSSI at the femto node and the received pilot strength determiner 228may measure RSCP at the femto node.

The femto node “i” may determine whether Ecp/Io_i is less than or equalto a threshold to determine whether coverage for the access terminal “i”is acceptable. If coverage is acceptable, the operational flow mayreturn back to block 904 where the femto node “i” waits to receive thenext neighbor report. In this way, the femto node may repeatedly monitorconditions at its home access terminals over time.

If coverage is not acceptable at block 908, the femto node “i” maycommence operations to adjust the transmit power of one or moreneighboring femto nodes. Initially, as represented by block 910, thefemto node “i” may set its transmit power to the maximum allowed value(e.g., the maximum value discussed at block 902). Here, the transmitpower of the femto node “i” may have been reduced after it was set themaximum value at block 902, for example, if the femto node “i” hadobeyed an intervening request from a neighboring femto node to reduceits transmit power. In some implementations, after increasing thetransmit power, the femto node “i” may determine whether the coveragefor the access terminal “i” is now acceptable. If so, the operationalflow may return back to block 904 as discussed above. If not, theoperational flow may proceed to block 912 as discussed below. In someimplementations the femto node “i” may perform the following operationswithout checking the effect of block 910.

As represented by block 912, the femto node “i” (e.g., the transmitpower controller 208) may rank the femto nodes in the neighbor report bythe strength of their corresponding RSCPs as measured by the accessterminal. A ranked list of the potentially interfering nodes 246 maythen be stored in the data memory 212. As will be discussed below, theoperational block 912 may exclude any neighboring femto node that hassent a NACK in response to a request to reduce transmit power and wherea timer associated with that NACK has not yet expired.

As represented by block 914, the femto node “i” (e.g., the transmitpower controller 208) selects the strongest interfering neighboringfemto node (e.g., femto node “j”) and determines by how much that femtonode should reduce its transmit power to maintain a given Ecp/Io foraccess terminal “i” at the designated coverage radius (path loss). Insome aspects the amount (e.g., percentage) of power reduction may berepresented by a parameter alpha_p. In some aspects, the operations ofblock 914 may involve determining whether Ecp/Io_i is greater than orequal to a threshold as discussed above.

Next, the femto node “i” (e.g., the transmitter 204 and thecommunication controller 210) sends a message to the femto node “j”requesting it to lower its power by the designated amount (e.g.,alpha_p). Sample operations that the femto node “j” may perform uponreceipt of such request are described below in conjunction with FIG. 10.

As represented by block 916, the femto node “i” (e.g., the receiver 206and the communication controller 210) will receive a message from thefemto node “j” in response to the request of block 914. In the event thefemto node “j” elected to reduce its transmit power by the requestedamount, the femto node “j” will respond to the request with anacknowledgment (ACK). In this case, the operational flow may return toblock 904 as described above.

In the event the femto node “j” elected to not reduce its transmit powerby the requested amount, the femto node “j” will respond to the requestwith a negative acknowledgment (NACK). In its response, the femto node“j” may indicate that it did not reduce its power at all or that itreduced its power by a given amount less than the requested amount. Inthis case, the operational flow may return to block 912 where the femtonode “i” may re-rank the femto nodes in the neighbor report according tothe RSCP measured by the access terminal “i” (e.g., based on a newlyreceived neighbor report). Here, however, the femto node “j” will beexcluded from this ranking as long as the timer associated with its NACKhas not expired. The operations of blocks 912 through 918 may thus berepeated until the femto node “i” determines that the Ecp/Io for theaccess terminal “i” is at the target value or has improved as much aspossible.

FIG. 10 illustrates sample operations that may be performed by a femtonode that receives a request to reduce transmit power. The receipt ofsuch a request is represented by block 1002. In an implementation wherethe node 200 of FIG. 2 is also capable of performing these operations,the operations of block 1002 may be performed at least in part by thereceiver 206 and the communication controller 210, the operations ofblocks 1004-1008 and 1012-1014 may be performed at least in part by thetransmit power controller 208, and the operations of blocks 1010 may beperformed at least in part by the transmitter 204 and the communicationcontroller 210.

At blocks 1004 and 1006, the femto node determines whether coverage forone or more home access terminals will be acceptable if the transmitpower is adjusted as requested. For example, the femto node “j” mayevaluate a request to lower its transmit power to alpha_p*HNB_Tx_j bydetermining whether each of its access terminals may pass a test similarto the test of described at block 906. Here, the femto node “j” maydetermine whether the Ecp/Io of an associated access terminal at adesignated coverage radius is greater than or equal to a thresholdvalue.

If coverage is acceptable at block 1006, the femto node “j” reduces itstransmit power by the requested amount for a defined period of time(block 1008). At block 1010, the femto node “j” responds to the requestwith an ACK. The operational flow may then return to block 1002 wherebythe femto node processes any additional requests to reduce transmitpower as they are received.

If coverage is not acceptable at block 1006, the femto node “j”determines how much it may lower its transmit power such that the testof block 1004 passes (block 1012). Here, it should be appreciated thatin some cases the femto node “j” may elect to not reduce its transmitpower at all.

At block 1014, the femto node “j” reduces its transmit power by theamount determined at block 1012, if applicable, for a defined period oftime. This amount may be represented by, for example, the valuebeta_p*HNB_Tx_j.

At block 1016, the femto node “j” will then respond to the request witha negative acknowledgment (NACK). In its response, the femto node “j”may indicate that it did not reduce its power at all or that it reducedits power by a given amount (e.g., beta_p*HNB_Tx_j). The operationalflow may then return to block 1002 as described above.

In some implementations, the femto node “i” and the femto node “j”maintain respective timers that count for a defined period time inconjunction with an ACK or a NACK. Here, after its timer expires, thefemto node “j” may reset its transmit power back to the previous level.In this way, the femto node “j” may avoid being penalized in the eventthe femto node “i” has moved.

Also, in some cases each femto node in the network may store themeasurements (e.g., the neighbor reports) that it received from anaccess terminal the last time the access terminal connected with thefemto node. In this way, in the event no access terminals are currentlyconnected to the femto node, the femto node may calculate a minimumtransmit power to ensure Ecp/Io coverage for initial acquisition.

If the femto node has sent requests to all neighboring femto nodes toreduce their power and cannot yet maintain the desired coverage at thespecified coverage radius, the femto node may calculate how much itscommon pilot Ec/Ior needs to be increased above its default level toreach the target coverage. The femto node may then raise the fraction ofits pilot power accordingly (e.g., within a preset maximum value).

An implementation that utilizes a scheme such as the one described aboveto maintain a coverage radius may thus be used to effectively settransmit power values in a network. For example, such a scheme may set alower bound on the geometry (and throughput) an access terminal willhave if it is within the designated coverage radius. Moreover, such ascheme may result in power profiles being more static whereby a powerprofile may only change when a femto node is added to or removed fromthe network. In some implementations, to eliminate further CPICH outagethe above scheme may be modified such that the CPICH Ec/Ior is adaptedaccording to measurements collected at the femto node.

A given femto node may perform the operations of blocks 904-918 for allof its associated access terminals. If more than one access terminal isassociated with a femto node, the femto node may send a request to aninterfering femto node whenever any one of its associated accessterminals is being interfered with.

Similarly when evaluating whether or not to respond to a request toreduce transmit power, a femto node performs the test of block 1004 forall its associated access terminals. The femto node may then select theminimum power that will guarantee an acceptable performance to all itsassociated access terminals.

In addition, each femto node in the network may perform these operationsfor its respective access terminals. Hence, each node in the network maysend a request to a neighboring node to reduce transmit power or mayreceive a request from a neighboring node to reduce transmit power. Thefemto nodes may perform these operations in an asynchronous manner withrespect to one another.

As mentioned above, in some implementations a quality of servicecriterion (e.g., throughput) may be employed to determine whether toreduce transmit power of a femto node. Such a scheme may be employed inaddition to or instead of the above scheme.

In a similar manner as discussed above, RSCP_i_j is defined as the CPICHRSCP of femto node “j” (HNB_j) as measured by access terminal “i”(HUE_i). RSSI_i is the RSSI as measured by access terminal “i.” Ecp/Io_iand Ecp/Nt_i, respectively, are the CPICH Ecp/Io and the CPICH SINR(signal to interference and noise ratio) of access terminal “i” from itsassociated femto node “i” (HNB_i). The femto node calculates thefollowing:

$\begin{matrix}{\left( {{Ecp}/{Io\_ i}} \right) = \frac{RSCP\_ i}{RSSI\_ i}} & {{EQUATION}\mspace{14mu} 21} \\{{SINR\_ i} = \frac{RSCP\_ i}{{RSSI\_ i} - {{RSCP\_ i}/\left( {{Ecp}/{Ior}} \right)}}} & {{EQUATION}\mspace{14mu} 22}\end{matrix}$

where Ecp/Ior is the ratio of the CPICH pilot transmit power to thetotal power of the cell.

The femto node estimates the Ecp/Io of the home access terminal if itwere at the edge of the femto node coverage corresponding to a path lossof PL_(HNB) _(_) _(coverage):

$\begin{matrix}{\left( {{{Ecp}/{Io\_ i}}\_} \right)_{HNB\_ Coverage} = \frac{{RSCP\_ i}{\_ i}_{HNB\_ Coverage}}{RSSI\_ i}} & {{EQUATION}\mspace{14mu} 23}\end{matrix}$

where RSCP_i_i_(HNB) _(_) _(Coverage) is the received pilot strength ataccess terminal “i” from its own femto node “i” at the edge of the femtonode “i” coverage. The edge of coverage corresponds to a path loss (PL)from the femto node equal PL_(HNB) Coverage andRSCP_i_i _(HNB) _(_) _(Coverage)=HNB_Tx_i*(Ecp/Ior)/PL_(HNB) _(_)_(Coverage)  EQUATION 24

Let (Ecp/Io)_Trgt_A be a threshold on the CPICH Ecp/Io preconfigured inthe femto node. The femto node checks the following:(Ecp/Io_i)_(HNB) _(_) _(Coverage)>(Ecp/Io)_Trgt_A?  EQUATION 25

If the answer is YES, the femto node does not send a request to reducetransmit power. If the answer is NO, the femto node sends a request toreduce transmit power as described below. In addition, or alternatively,the femto node may perform a similar test relating to throughput (e.g.,SINR_i).

The femto node sets its power to the maximum allowed by the macro cellcoverage hole condition.

The femto node “i” ranks the neighbor cells in descending order of thehome access terminal's reported RSCP.

The femto node “i” picks the neighbor cell femto node “j” with thehighest RSCP value, RSCP_i_j.

The serving femto node “i” calculates how much femto node “j” needs tolower its transmit power such that the performance of its accessterminal “i” improves. Let (Ecp/Io)_Trgt_A be a target CPICH Ecp/Io forthe home access terminal that is preconfigured in the femto node. Thistarget Ecp/Io can be chosen such that home access terminals are not inoutage. It can also be more aggressive to guarantee a minimum geometryof the home access terminals to maintain a certain data throughput orperformance criteria. The desired RSCP_i_j_trgt seen by access terminal“i” from neighbor femto node “j” to maintain (Ecp/Io) Trgt_A may becalculated as:

$\begin{matrix}{{{RSCP\_ i}{\_ j}{\_ Trgt}} = {\frac{\left( {{Ecp}/{Ior}} \right)*{RSCP\_ i}{\_ i}_{HNB\_ Coverage}}{\left( {{Ecp}/{Io}} \right){\_ Trgt}{\_ A}} - {\left( {{Ecp}/{Ior}} \right)*{RSSI\_ i}} + {{RSCP\_ i}{\_ j}}}} & {{EQUATION}\mspace{14mu} 26}\end{matrix}$

In addition, or alternatively, the femto node may perform a similar testrelating to throughput. The femto node “i” calculates the ratioalpha_p_j by which femto node “j” should lower its power as:alpha_p_j=RSCP_i_j_Trgt/RSCP_i_j  EQUATION 27

The femto node “i” sends a request to femto node “j” to lower itstransmit power by a ratio alpha_p_j. As discussed herein this requestmay be sent through upper layer signaling (backhaul) to a centralizedalgorithm or sent to femto node “j” directly from femto node “i.”

The femto node “j” evaluates whether it may respond to the request offemto node “i” by making its transmit powerHNB_Tx_new_j=alpha_p_j*HNB_Tx_j, where HNB_Tx_j is set as above. In someimplementations the femto node “j” checks two tests.

Test 1: This test is based on the scheme previously described for FIG.9. The CPICH Ecp/Io of an associated home access terminal, which is awayfrom the femto node “j” by the coverage radius, is above a certainthreshold (Ecp/Io)_Trgt_B. This test is to guarantee that its own UEhave an acceptable performance within a certain radius around the femtonode and another registered home access terminal can also acquire thefemto node. This is calculated as follows:

$\begin{matrix}{\left( {{Ecp}/{Io\_ j}} \right)_{HNB\_ Coverage} = \frac{{RSCP\_ j}{\_ j}_{HNB\_ Coverage}}{RSSI\_ j}} & {{EQUATION}\mspace{14mu} 28}\end{matrix}$

where RSSI_j and RSCP_j_j are the RSSI and RSCP reported by HUE_j at thecoverage radius (or otherwise estimated by HNB_j) to femto node “j”before transmit power modification. The test is(Ecp/Io_j)_(HNB) _(_) _(Coverage)>(Ecp/Io)_Trgt_B?  EQUATION 29

Test 2: The CPICH SINR of HUE_j is greater than a certain target tomaintain a certain performance criterion (e.g., quality of service suchas throughput):SINR_new_j>SINR_Trgt?  EQUATION 30

where

$\begin{matrix}{{{SINR\_ new}{\_ j}} = \frac{{alpha\_ p}{\_ j}*{RSCP\_ j}{\_ j}}{{RSSI\_ j} - {{RSCP\_ j}{{\_ j}/\left( {{Ecp}/{Ior}} \right)}}}} & {{EQUATION}\mspace{14mu} 31}\end{matrix}$

If either or both tests pass (depending on the particularimplementation), femto node “j” lowers its transmit power to bealpha_p_j*HNB_Tx_j and sends an ACK to femto node “i”, given that thenew power is above the minimum allowed (e.g. −20 dBm).

If one or both tests fail, femto node “j” does not lower its transmitpower to the required value. Instead, it calculates how much it canlower its transmit power without hurting its performance. In otherwords, in an implementation that uses both tests, the femto node maycalculate its new transmit powers such that both Test 1 and Test 2 passand lowers its transmit power to the higher of the two. However, if withthe current femto node “j” power settings either test fails, then femtonode “j” does not lower its power. The femto nodes may also lower theirpower to a minimum standardized limit (e.g., as discussed herein). Inall these cases, femto node “j” may report a NACK to femto node “i” withits final power settings.

The algorithms discussed above allow femto nodes to adaptively adjusttheir transmit powers in a collaborative fashion. These algorithm havemany parameters which can be adjusted (e.g., by an operator) such as,for example, Ecp/Io_Trgt_A, Coverage_radius, Ecp/Io_Trgt_B, SINR_Trgt,and the timers. The algorithms may be further refined by making thethresholds adapted by a learning process.

In some aspects, the timers may be varied (e.g., independently) tooptimize system performance. If an access terminal “i” is not connectedto a femto node “i,” and femto node “j” is already transmitting toaccess terminal “j,” access terminal “i” may not be able to acquirefemto node “i” due to its low CPICH Ecp/Io. The above algorithm may thenbe modified such that each femto node tries to maintain a minimum CPICHEcp/Io within a certain radius around the femto node. A disadvantage ofthis is that neighbor access terminal “j” may be penalized while femtonode “i” has no access terminal associated with it. To avoidcontinuously penalizing neighbor femto nodes, femto node “i” will sendin its request to neighbor femto node “j” an indication that thisrequest is for initial acquisition. If femto node “j” responds bylowering its power, it sets a timer and femto node “i” sets a largertimer. The femto node “j” will reset its transmit power to its defaultvalue after its timer expires but femto node “i” will not send anotherrequest (for initial acquisition) to femto node “j” until the timer forfemto node “i” expires. An issue remains in that femto node “i” may haveto estimate the RSSI_i as there is not an access terminal associatedwith it. The femto node “i” also may have to estimate the neighboringinterferers RSCP_j. However, the strongest interferers the femto nodessee are not necessarily the strongest interferers its access terminalswill see.

To alleviate the initial acquisition problem, access terminals may alsobe allowed to camp in idle mode on neighboring femto nodes with the samePLMN_ID. The access terminals may read the neighbor list on the campedfemto node which may contain the scrambling code and timing of its ownfemto node. This can put the access terminal at an advantage whenacquiring its femto node at negative geometries.

Referring now to FIGS. 11-13B, implementations that employ a centralizedpower controller to control the transmit power of femto nodes aredescribed. FIG. 11 illustrates a sample system 1100 including acentralized controller 1102, femto nodes 1104, and access terminals1106. Here, femto node 1104A is associated with access terminal 1106Aand femto node 1104B is associated with access terminal 1106B. Thecentralized power controller 1102 includes a transceiver 1110 (withtransmitter 1112 and receiver 1114 components) as well as a transmitpower controller 1116. In some aspects, these components may providefunctionality similar to the functionality of the similarly namedcomponents of FIG. 2.

FIG. 12 describes various operations that may be performed in animplementation where a femto node (e.g., femto node 1104A) simplyforwards the neighbor list information it receives from its associatedaccess terminal (e.g., access terminal 1106A) to the centralized powercontroller 1102. The centralized power controller 1102 may then performoperations similar to those described above to request a femto node(e.g., femto node 1104B) that is in the vicinity of the femto node 1104Ato reduce its transmit power.

The operations blocks 1202 and 1204 may be similar to the operations ofblocks 902 and 904 discussed above. At block 1206, the femto node 1104Aforwards a neighbor list 1108A it receives from the access terminal1106A to the centralized power controller 1102. The operations of blocks1202-1206 may be repeated on a regular basis (e.g., periodically)whenever the femto node 1104A receives a neighbor report from the accessterminal 1106A.

As represented by block 1208, the centralized power controller 1102 mayreceive similar information from other femto nodes in the network. Atblock 1210, the centralized power controller 1102 may then performoperations similar to those discussed above (e.g., at block 906) todetermine whether a femto node should reduce its transmit power. In someaspects, the centralized power controller 1102 may make a power controldecision based on information it receives relating to conditions atmultiple femto nodes. For example, if a given femto node is interferingwith several other femto nodes, the centralized power controller 1102may attempt to reduce the power of that femto node first.

At block 1212, the centralized power controller 1102 sends a message toeach femto node that the centralized controller 1100 determines shouldreduce its transmit power. As above, this request may indicate thedegree to which a designated femto node should reduce its power. Theseoperations may be similar to the operations of blocks 912 and 914.

The centralized power controller 1102 receives responses from the femtonodes at block 1214. As represented by block 1216, if no NACKs arereceived in response to the requests issued at block 1212, theoperational flow for the centralized power controller 1102 returns toblock 1208 where the centralized controller 1102 continues to receiveinformation from the femto nodes in the network and performs the powercontrol operations described above.

If, on the other hand, one or more NACKs are received in response to therequests issued at block 1212, the operational flow for the centralizedpower controller 1102 returns to block 1210 where the centralizedcontroller 1102 may identify other femto nodes that should reduce theirtransmit power and then sends out new power control messages. Again,these operations may be similar to blocks 912 and 914 discussed above.

FIGS. 13A and 13B describe various operations that may be performed inan implementation where a femto node (e.g., femto node 1104A) identifiesa neighboring femto node (e.g., femto node 1104B) that should reduce itspower and sends this information to the centralized power controller1102. The centralized power controller 1102 may then send a request tothe femto node 1104B to reduce its transmit power.

The operations blocks 1302-1312 may be similar to the operations ofblocks 902-912 discussed above. At block 1314, the femto node 1104Asends a message identifying the femto node 1104B to the centralizedpower controller 1102. Such a message may take various forms. Forexample, the message may simply identify a single femto node (e.g.,femto node 1104B) or the message may comprise a ranking of femto nodes(e.g., as described above at block 912). Such a list also may includesome or all of the neighbor report the femto node 1104A received fromthe access terminal 1106A. The operations of blocks 1302-1314 may berepeated on a regular basis (e.g., periodically) whenever the femto node1104A receives a neighbor report from the access terminal 1106A.

As represented by block 1316, the centralized power controller 1102 mayreceive similar information from other femto nodes in the network. Atblock 1318, the centralized power controller 1102 may determine whetherit should make any adjustments to any requests for reduction in transmitpower it receives (e.g., based on other requests it receives requestinga reduction in power for the same femto node).

At block 1320, the centralized power controller 1102 may then send amessage to each femto node that the centralized controller 1102determines should to reduce its power. As above, this request mayindicate the degree to which the designated femto node should reduce itspower.

The centralized power controller 1102 receives responses from the femtonodes at block 1322. As represented by block 1324, if no NACKs arereceived in response to the requests issued at block 1320, theoperational flow for the centralized power controller 1102 returns toblock 1316 where the centralized controller 1102 continues to receiveinformation from the femto nodes in the network and performs the powercontrol operations described above.

If, on the other hand, one or more NACKs are received in response to therequests issued at block 1320, the operational flow for the centralizedpower controller 1102 returns to block 1318 where the centralizedcontroller 1102 may identify other femto nodes that should reduce theirtransmit power and then sends out new power control messages (e.g.,based on a ranked list received from the femto node 1104A).

In view of the above it should be appreciated that the teachings hereinmay provide an effective way of managing transmit power of neighboringaccess nodes. For example, in a static environment downlink transmitpowers of the femto nodes may be adjusted to a static value wherebyservice requirements at all access terminals may be satisfied.Consequently, such a solution to be compatible with legacy accessterminals since all channels may continuously be transmitted at constantpowers. In addition, in a dynamic environment transmit powers may bedynamically adjusted to accommodate the changing service requirements ofthe nodes in the system.

Connectivity for a femto node environment may be established in variousways. For example, FIG. 14 illustrates an exemplary communication system1400 where one or more femto nodes are deployed within a networkenvironment. Specifically, the system 1400 includes multiple femto nodes1410 (e.g., femto nodes 1410A and 1410B) installed in a relatively smallscale network environment (e.g., in one or more user residences 1430).Each femto node 1410 may be coupled to a wide area network 1440 (e.g.,the Internet) and a mobile operator core network 1450 via a DSL router,a cable modem, a wireless link, or other connectivity means (not shown).As discussed herein, each femto node 1410 may be configured to serveassociated access terminals 1420 (e.g., access terminal 1420A) and,optionally, other access terminals 1420 (e.g., access terminal 1420B).In other words, access to femto nodes 1410 may be restricted whereby agiven access terminal 1420 may be served by a set of designated (e.g.,home) femto node(s) 1410 but may not be served by any non-designatedfemto nodes 1410 (e.g., a neighbor's femto node 1410).

The owner of a femto node 1410 may subscribe to mobile service, such as,for example, 3G mobile service offered through the mobile operator corenetwork 1450. In addition, an access terminal 1420 may be capable ofoperating both in macro environments and in smaller scale (e.g.,residential) network environments. In other words, depending on thecurrent location of the access terminal 1420, the access terminal 1420may be served by an access node 1460 of the macro cell mobile network1450 or by any one of a set of femto nodes 1410 (e.g., the femto nodes1410A and 1410B that reside within a corresponding user residence 1430).For example, when a subscriber is outside his home, he is served by astandard macro access node (e.g., node 1460) and when the subscriber isat home, he is served by a femto node (e.g., node 1410A). Here, itshould be appreciated that a femto node 1410 may be backward compatiblewith existing access terminals 1420.

A femto node 1410 may be deployed on a single frequency or, in thealternative, on multiple frequencies. Depending on the particularconfiguration, the single frequency or one or more of the multiplefrequencies may overlap with one or more frequencies used by a macronode (e.g., node 1460).

An access terminal 1420 may be configured to communicate either with themacro network 1450 or the femto nodes 1410, but not both simultaneously.In addition, an access terminal 1420 being served by a femto node 1410may not be in a soft handover state with the macro network 1450.

In some aspects, an access terminal 1420 may be configured to connect toa preferred femto node (e.g., the home femto node of the access terminal1420) whenever such connectivity is possible. For example, whenever theaccess terminal 1420 is within the user's residence 1430, it may bedesired that the access terminal 1420 communicate only with the homefemto node 1410.

In some aspects, if the access terminal 1420 operates within the macrocellular network 1450 but is not residing on its most preferred network(e.g., as defined in a preferred roaming list), the access terminal 1420may continue to search for the most preferred network (e.g., thepreferred femto node 1410) using a Better System Reselection (“BSR”),which may involve a periodic scanning of available systems to determinewhether better systems are currently available, and subsequent effortsto associate with such preferred systems. With the acquisition entry,the access terminal 1420 may limit the search for specific band andchannel. For example, the search for the most preferred system may berepeated periodically. Upon discovery of a preferred femto node 1410,the access terminal 1420 selects the femto node 1410 for camping withinits coverage area.

The teachings herein may be employed in a wireless multiple-accesscommunication system that simultaneously supports communication formultiple wireless access terminals. As mentioned above, each terminalmay communicate with one or more base stations via transmissions on theforward and reverse links. The forward link (or downlink) refers to thecommunication link from the base stations to the terminals, and thereverse link (or uplink) refers to the communication link from theterminals to the base stations. This communication link may beestablished via a single-in-single-out system, amultiple-in-multiple-out (“MIMO”) system, or some other type of system.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min {N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system may provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

A MIMO system may support time division duplex (“TDD”) and frequencydivision duplex (“FDD”). In a TDD system, the forward and reverse linktransmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the forward link channel from thereverse link channel. This enables the access point to extract transmitbeam-forming gain on the forward link when multiple antennas areavailable at the access point.

The teachings herein may be incorporated into a node (e.g., a device)employing various components for communicating with at least one othernode. FIG. 15 depicts several sample components that may be employed tofacilitate communication between nodes. Specifically, FIG. 15illustrates a wireless device 1510 (e.g., an access point) and awireless device 1550 (e.g., an access terminal) of a MIMO system 1500.At the device 1510, traffic data for a number of data streams isprovided from a data source 1512 to a transmit (“TX”) data processor1514.

In some aspects, each data stream is transmitted over a respectivetransmit antenna. The TX data processor 1514 formats, codes, andinterleaves the traffic data for each data stream based on a particularcoding scheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by a processor 1530. A data memory 1532 may storeprogram code, data, and other information used by the processor 1530 orother components of the device 1510.

The modulation symbols for all data streams are then provided to a TXMIMO processor 1520, which may further process the modulation symbols(e.g., for OFDM). The TX MIMO processor 1520 then provides N_(T)modulation symbol streams to N_(T) transceivers (“XCVR”) 1522A through1522T. In some aspects, the TX MIMO processor 1520 applies beam-formingweights to the symbols of the data streams and to the antenna from whichthe symbol is being transmitted.

Each transceiver 1522 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transceivers 1522A through 1522T are thentransmitted from N_(T) antennas 1524A through 1524T, respectively.

At the device 1550, the transmitted modulated signals are received byN_(R) antennas 1552A through 1552R and the received signal from eachantenna 1552 is provided to a respective transceiver (“XCVR”) 1554Athrough 1554R. Each transceiver 1554 conditions (e.g., filters,amplifies, and downconverts) a respective received signal, digitizes theconditioned signal to provide samples, and further processes the samplesto provide a corresponding “received” symbol stream.

A receive (“RX”) data processor 1560 then receives and processes theN_(R) received symbol streams from N_(R) transceivers 1554 based on aparticular receiver processing technique to provide N_(T) “detected”symbol streams. The RX data processor 1560 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by the RX dataprocessor 1560 is complementary to that performed by the TX MIMOprocessor 1520 and the TX data processor 1514 at the device 1510.

A processor 1570 periodically determines which pre-coding matrix to use(discussed below). The processor 1570 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A datamemory 1572 may store program code, data, and other information used bythe processor 1570 or other components of the device 1550.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 1538,which also receives traffic data for a number of data streams from adata source 1536, modulated by a modulator 1580, conditioned by thetransceivers 1554A through 1554R, and transmitted back to the device1510.

At the device 1510, the modulated signals from the device 1550 arereceived by the antennas 1524, conditioned by the transceivers 1522,demodulated by a demodulator (“DEMOD”) 1540, and processed by a RX dataprocessor 1542 to extract the reverse link message transmitted by thedevice 1550. The processor 1530 then determines which pre-coding matrixto use for determining the beam-forming weights then processes theextracted message.

FIG. 15 also illustrates that the communication components may includeone or more components that perform power control operations as taughtherein. For example, a power control component 1590 may cooperate withthe processor 1530 and/or other components of the device 1510 tosend/receive signals to/from another device (e.g., device 1550) astaught herein. Similarly, a power control component 1592 may cooperatewith the processor 1570 and/or other components of the device 1550 tosend/receive signals to/from another device (e.g., device 1510). Itshould be appreciated that for each device 1510 and 1550 thefunctionality of two or more of the described components may be providedby a single component. For example, a single processing component mayprovide the functionality of the power control component 1590 and theprocessor 1530 and a single processing component may provide thefunctionality of the power control component 1592 and the processor1570.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (“CDMA”) systems,Multiple-Carrier CDMA (“MCCDMA”), Wideband CDMA (“W-CDMA”), High-SpeedPacket Access (“HSPA,” “HSPA+”) systems, High-Speed Downlink PacketAccess (“HSDPA”) systems, Time Division Multiple Access (“TDNM”)systems, Frequency Division Multiple Access (“FDMA”) systems,Single-Carrier FDMA (“SC-FDMA”) systems, Orthogonal Frequency DivisionMultiple Access (“OFDMA”) systems, or other multiple access techniques.A wireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network mayimplement a radio technology such as Universal Terrestrial Radio Access(“UTRA)”, cdma2000, or some other technology. UTRA includes W-CDMA andLow Chip Rate (“LCR”). The cdma2000 technology covers IS-2000, IS-95 andIS-856 standards. A TDMA network may implement a radio technology suchas Global System for Mobile Communications (“GSM”). An OFDMA network mayimplement a radio technology such as Evolved UTRA (“E-UTRA”), IEEE802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, andGSM are part of Universal Mobile Telecommunication System (“UMTS”). Theteachings herein may be implemented in a 3GPP Long Term Evolution(“LTE”) system, an Ultra-Mobile Broadband (“UMB”) system, and othertypes of systems. LTE is a release of UMTS that uses E-UTRA. Althoughcertain aspects of the disclosure may be described using 3GPPterminology, it is to be understood that the teachings herein may beapplied to 3GPP (Re199, Re15, Re16, Re17) technology, as well as 3GPP2(IxRTT, 1×EV-DO RelO, RevA, RevB) technology and other technologies.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., nodes). For example, anaccess node as discussed herein may be configured or referred to as anaccess point (“AP”), base station (“BS”), NodeB, radio networkcontroller (“RNC”), eNodeB, base station controller (“BSC”), basetransceiver station (“BTS”), transceiver function (“TF”), radio router,radio transceiver, basic service set (“BSS”), extended service set(“ESS”), radio base station (“RBS”), a femto node, a pico node, or someother terminology.

In addition, an access terminal as discussed herein may be referred toas a mobile station, user equipment, subscriber unit, subscriberstation, remote station, remote terminal, user terminal, user agent, oruser device. In some implementations such a node may consist of, beimplemented within, or include a cellular telephone, a cordlesstelephone, a Session Initiation Protocol (“SIP”) phone, a wireless localloop (“WLL”) station, a personal digital assistant (“PDA”), a handhelddevice having wireless connection capability, or some other suitableprocessing device connected to a wireless modem.

Accordingly, one or more aspects taught herein may consist of, beimplemented within, or include variety types of apparatuses. Such anapparatus may comprise a phone (e.g., a cellular phone or smart phone),a computer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a globalpositioning system device, or any other suitable device that isconfigured to communicate via a wireless medium.

As mentioned above, in some aspects a wireless node may comprise anaccess node (e.g., an access point) for a communication system. Such anaccess node may provide, for example, connectivity for or to a network(e.g., a wide area network such as the Internet or a cellular network)via a wired or wireless communication link. Accordingly, the access nodemay enable another node (e.g., an access terminal) to access the networkor some other functionality. In addition, it should be appreciated thatone or both of the nodes may be portable or, in some cases, relativelynon-portable. Also, it should be appreciated that a wireless node (e.g.,a wireless device) also may be capable of transmitting and/or receivinginformation in a non-wireless manner via an appropriate communicationinterface (e.g., via a wired connection).

A wireless node may communicate via one or more wireless communicationlinks that are based on or otherwise support any suitable wirelesscommunication technology. For example, in some aspects a wireless nodemay associate with a network. In some aspects the network may comprise alocal area network or a wide area network. A wireless device may supportor otherwise use one or more of a variety of wireless communicationtechnologies, protocols, or standards such as those discussed herein(e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, awireless node may support or otherwise use one or more of a variety ofcorresponding modulation or multiplexing schemes. A wireless node maythus include appropriate components (e.g., air interfaces) to establishand communicate via one or more wireless communication links using theabove or other wireless communication technologies. For example, awireless node may comprise a wireless transceiver with associatedtransmitter and receiver components that may include various components(e.g., signal generators and signal processors) that facilitatecommunication over a wireless medium.

The components described herein may be implemented in a variety of ways.Referring to FIGS. 16-19, apparatuses 1600-1900 are represented as aseries of interrelated functional blocks. In some aspects thefunctionality of these blocks may be implemented as a processing systemincluding one or more processor components. In some aspects thefunctionality of these blocks may be implemented using, for example, atleast a portion of one or more integrated circuits (e.g., an ASIC). Asdiscussed herein, an integrated circuit may include a processor,software, other related components, or some combination thereof. Thefunctionality of these blocks also may be implemented in some othermanner as taught herein. In some aspects one or more of the dashedblocks in FIGS. 16-19 are optional.

The apparatuses 1600-1900 may include one or more modules that mayperform one or more of the functions described above with regard tovarious figures. For example, a maximum received signal strengthdetermining means 1602 may correspond to, for example, a signal strengthdeterminer as discussed herein. A minimum coupling loss determiningmeans 1604 may correspond to, for example, a coupling loss determiner asdiscussed herein. A transmit power determining means 1606, 1704, or 1804may correspond to, for example, a transmit power controller as discussedherein. A total received signal strength determining means 1702 maycorrespond to, for example, a signal strength determiner as discussedherein. A received pilot signal strength determining means 1706 maycorrespond to, for example, a received pilot strength determiner asdiscussed herein. An error determining means 1708 may correspond to, forexample, an error determiner as discussed herein. A node in coveragearea determining means 1710 may correspond to, for example, a nodedetector as discussed herein. A node identifying means 1712 or 1806 maycorrespond to, for example, a node detector as discussed herein. Asignal-to-noise ratio determining means 1706 or 1808 may correspond to,for example, a signal-to-noise ratio determiner as discussed herein. Achannel quality determining means 1802 may correspond to, for example, achannel quality determiner as discussed herein. A receiving means 1902may correspond to, for example, a receiver as discussed herein. Anidentifying means 1904 may correspond to, for example, a transmit powercontroller as discussed herein. A transmitting means 1906 may correspondto, for example, a transmitter as discussed herein.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations may be used herein as a convenient method of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements may be employed there or that the first element must precedethe second element in some manner. Also, unless stated otherwise a setof elements may comprise one or more elements.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that any of the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by an integrated circuit (“IC”), an access terminal,or an access point. The IC may comprise a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, electrical components, optical components,mechanical components, or any combination thereof designed to performthe functions described herein, and may execute codes or instructionsthat reside within the IC, outside of the IC, or both. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored on or transmitted over as one or moreinstructions or code on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that facilitates transfer of a computer programfrom one place to another. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. In summary, it should be appreciated that acomputer-readable medium may be implemented in any suitablecomputer-program product.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of thedisclosure. Thus, the present disclosure is not intended to be limitedto the aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method of wireless communication, comprising:identifying that a visitor access terminal that is not authorized tohandoff to a non-macro base station has entered into a non-macrocoverage area for the non-macro base station; determining a channelquality value associated with a channel used by the visitor accessterminal; and determining, by a transmit power controller in response tothe identifying, a transmit power value including a reduced maximumtransmission power level at which the non-macro base station ispermitted to transmit to a home subscriber terminal that is based on thedetermined channel quality value and is configured to limit interferencecaused by the non-macro base station upon the visitor access terminal.2. The method of claim 1, wherein the determination of the transmitpower value comprises adjusting the transmit power value based on achange in the determined channel quality value or based on a comparisonof the determined channel quality value with a threshold.
 3. The methodof claim 1, wherein the determination of the channel quality valuecomprises receiving an indication of channel quality from the homesubscriber terminal.
 4. The method of claim 1, further comprising:identifying that the home subscriber terminal is located substantiallynear an edge of the non-macro coverage area for the non-macro basestation, wherein the determination of the transmit power value isfurther based upon an estimated distance between the non-macro basestation and the edge of the non-macro coverage area, wherein thedetermined channel quality value corresponds to a signal-to-noise ratioassociated with the home subscriber terminal; and wherein the transmitpower value is determined based on the determined signal-to-noise ratioand a defined maximum signal-to-noise ratio.
 5. The method of claim 4,wherein the determination of the signal-to-noise ratio comprisesreceiving signal-to-noise ratio information from the home subscriberterminal.
 6. The method of claim 4, wherein the determination that thehome subscriber terminal is located substantially near the edge of thecoverage area for the non-macro base station is based on a path lossbetween the home subscriber terminal and the non-macro base station. 7.The method of claim 1, wherein the visitor subscriber terminal isrestricted for least one of the group consisting of: signaling, dataaccess, registration, paging, and service to the non-macro base station.8. The method of claim 1, wherein the reduced maximum transmission powerlevel is established for a common control channel, and wherein thedetermined channel quality value indicates quality associated with thecommon control channel.
 9. The method of claim 1, wherein the transmitpower value comprises a downlink transmit power value for the non-macrobase station.
 10. The method of claim 1, wherein the reduced maximumtransmission power level corresponds to a first preliminary maximumtransmit power value, the method further comprising: determining atleast one other preliminary maximum transmit power value; anddetermining the reduced maximum transmit power value based on a minimumof the first and at least one other preliminary maximum transmit powervalues.
 11. The method of claim 1, wherein the channel quality value andthe transmit power value are determined on a repeated basis.
 12. Themethod of claim 1, wherein the non-macro base station corresponds to afemto node or a pico node.
 13. The method of claim 1, wherein anestimated distance between the non-macro base station and the edge ofthe non-macro coverage area for the non-macro base station is used inconjunction with the determined channel quality value to calculate thereduced maximum transmission power level.
 14. The method of claim 1,wherein the channel quality value is a predefined path loss valueindicative of path loss between the non-macro base station and an edgeof the non-macro coverage area, or wherein the channel quality value isbased on an indication of path loss on the channel to a first homesubscriber terminal of the non-macro base station, or wherein thechannel quality value is independently calculated at the non-macro basestation based on a measurement report from a second home subscriberterminal.
 15. An apparatus for wireless communication, comprising: anode detector configured to identify that a visitor access terminal thatis not authorized to handoff to a non-macro base station has enteredinto a non-macro coverage area for the non-macro base station; a channelquality determiner configured to determine a channel quality valueassociated with a channel used by the visitor access terminal; and atransmit power controller configured to determine, in response to theidentification, a transmit power value including a reduced maximumtransmission power level at which the non-macro base station ispermitted to transmit to a home subscriber terminal that is based on thedetermined channel quality value and is configured to limit interferencecaused by the non-macro base station upon the visitor access terminal.16. The apparatus of claim 15, wherein the determination of the transmitpower value comprises adjusting the transmit power value based on achange in the determined channel quality value or based on a comparisonof the determined channel quality value with a threshold.
 17. Theapparatus of claim 15, wherein the determination of the channel qualityvalue comprises receiving an indication of channel quality from the homesubscriber terminal.
 18. The apparatus of claim 15, wherein the nodedetector is further configured to identify that the home subscriberterminal is substantially near an edge of the non-macro coverage area ofthe non-macro base station; a signal-to-noise ratio determinerconfigured to determine a signal-to-noise ratio associated with the homesubscriber terminal based on the determined channel quality value,wherein the transmit power value is determined based on the determinedsignal-to-noise ratio and a defined maximum signal-to-noise ratio,wherein the transmit power value is determined further based upon anestimated distance between the non-macro base station and the edge ofthe non-macro coverage area.
 19. The apparatus of claim 18, wherein thedetermination of the signal-to-noise ratio comprises receivingsignal-to-noise ratio information from the home subscriber terminal. 20.The apparatus of claim 15, wherein the visitor subscriber terminal isrestricted for least one of the group consisting of: signaling, dataaccess, registration, paging, and service to the non-macro base station.21. The apparatus of claim 15, wherein the reduced maximum transmissionpower level is established for a common control channel, and wherein thedetermined channel quality value indicates quality associated with thecommon control channel.
 22. The apparatus of claim 15, wherein thenon-macro base station corresponds to a femto node or a pico node. 23.An apparatus for wireless communication, comprising: means foridentifying that a visitor access terminal that is not authorized tohandoff to a non-macro base station has entered into a non-macrocoverage area for the non-macro base station; means for determining achannel quality value associated with a channel used by the visitoraccess terminal; and means for determining, in response to theidentification, a transmit power value including a reduced maximumtransmission power level at which the non-macro base station ispermitted to transmit to a home subscriber terminal that is based on thedetermined channel quality value and is configured to limit interferencecaused by the non-macro base station upon the visitor access terminal.24. The apparatus of claim 23, wherein the determination of the transmitpower value comprises adjusting the transmit power value based on achange in the determined channel quality value or based on a comparisonof the determined channel quality value with a threshold.
 25. Theapparatus of claim 23, wherein the determination of the channel qualityvalue comprises receiving an indication of channel quality from the homesubscriber terminal.
 26. The apparatus of claim 23, wherein the meansfor identifying identifies that the home subscriber terminal that issubstantially near an edge of the non-macro coverage area for thenon-macro base station, means for determining a signal-to-noise ratioassociated with the home subscriber terminal based on the determinedchannel quality value, wherein the transmit power value is determinedbased on the determined signal-to-noise ratio and a defined maximumsignal-to-noise ratio, wherein the transmit power value is determinedfurther based upon an estimated distance between the non-macro basestation and the edge of the non-macro coverage area.
 27. The apparatusof claim 26, wherein the determination of the signal-to-noise ratiocomprises receiving signal-to-noise ratio information from the homesubscriber terminal.
 28. The apparatus of claim 23, wherein the visitorsubscriber terminal is restricted for least one of the group consistingof: signaling, data access, registration, paging, and service to thenon-macro base station.
 29. The apparatus of claim 23, wherein thereduced maximum transmission power level is established for a commoncontrol channel, and wherein the determined channel quality valueindicates quality associated with the common control channel.
 30. Theapparatus of claim 23, wherein the non-macro base station corresponds toa femto node or a pico node.
 31. A non-transitory computer-readablemedium containing instructions stored thereon, which, when executed by acomputer, cause the computer to perform operations, the instructionscomprising: program code to identify that a visitor access terminal thatis not authorized to handoff to a non-macro base station has enteredinto a non-macro coverage area for the non-macro base station: programcode to determine a channel quality value associated with a channel usedby the visitor access terminal; and program code to determine, inresponse to the identification, a transmit power value including areduced maximum transmission power level at which the non-macro basestation is permitted to transmit to a home subscriber terminal that isbased on the determined channel quality value and is configured to limitinterference caused by the non-macro base station upon the visitoraccess terminal.
 32. The non-transitory computer-readable medium ofclaim 31, wherein the determination of the transmit power valuecomprises adjusting the transmit power value based on a change in thedetermined channel quality value or based on a comparison of thedetermined channel quality value with a threshold.
 33. Thenon-transitory computer-readable medium of claim 31, wherein thedetermination of the channel quality value comprises receiving anindication of channel quality from the home subscriber terminal.
 34. Thenon-transitory computer-readable medium of claim 31, further comprising:program code to identify that the home subscriber terminal is locatedsubstantially near an edge of the non-macro coverage area for thenon-macro base station, program code to determine a signal-to-noiseratio associated with the home subscriber terminal based on thedetermined channel quality value, wherein the transmit power value isdetermined based on the determined signal-to-noise ratio and a definedmaximum signal-to-noise ratio, wherein the transmit power value isdetermined further based upon an estimated distance between thenon-macro base station and the edge of the non-macro coverage area. 35.The non-transitory computer-readable medium of claim 34, wherein thedetermination of the signal-to-noise ratio comprises receivingsignal-to-noise ratio information from the home subscriber terminal. 36.The non-transitory computer-readable medium of claim 31, wherein thevisitor subscriber terminal is restricted for least one of the groupconsisting of: signaling, data access, registration, paging, and serviceto the non-macro base station.
 37. The non-transitory computer-readablemedium of claim 31, wherein the reduced maximum transmission power levelis established for a common control channel, and wherein the determinedchannel quality value indicates quality associated with the commoncontrol channel.
 38. The non-transitory computer-readable medium ofclaim 31, wherein the non-macro base station corresponds to a femto nodeor a pico node.